ADHD software dev here. I read both the other replies, and they are good, I +1 all of their advice, but I'd like to throw in my two cents. This is the internet so I'm sure I'll get a lot of replies telling me how wrong I am, but these are all things that have helped me be successful in my personal life.
I am not a doctor (obviously) and ultimately you should listen to what your healthcare provider tells you to do, not a stranger on the internet. But I will say in my opinion medication can be helpful but is not necessarily mandatory for you to be cope and be functional. I tried quite a few ADHD meds and discovered the non-stimulant ones don't do very much, and the stimulants cause so many negative health side effects they outweigh the intended positive primary effect. The hypertension is ridiculous (who cares how productive you are if you're about to have a stroke in your 20s?), and the mood/social effects suck too. It's fine if I'm working in a vacuum but if I get quiet and introverted and inside my head and grumpy but I have to work collaboratively with other people, it's really tough and now it's an entirely different problem that needs to be addressed. So I decided to just go med-free and try to find other ways to deal.
Get good sleep. Ideally, you want 8 hours and a fixed bedtime every night. Sometimes this sucks because staying up all night can be fun but it throws off your rhythm and you'll be impacted for days. Once you get into a solid schedule and it starts feeling natural, you'll see how big a difference it can make. (This is also a part that can be very easily thrown out of whack by meds.)
Eat breakfast. You want to have a good meal to start your day, your brain needs it to function. Don't eat cereal, you'll kickstart your metabolism but without getting many nutrients and just end up hungry hours before lunchtime. I have had the best luck with foods high in protein and fat, like eggs and bacon and avocado for instance. You'll be full longer than usual and have more mental clarity.
Exercise regularly. Building up your body also builds up your mind. If you can run, swim, bike, lift, yoga, soccer, [insert exercise you enjoy here], this will help a lot. You need to do this regularly, I'd suggest 3-6 days a week, usually, you want to have a day off for body to recover. This burns off a lot of your excess energy. Exercising after work gives you something to look forward to, but can be hard to do when you're mentally tired from working and just want to chill. Exercise before work is hard to make yourself do because waking up early sucks, but you'll feel SO much better the whole day, and you start your day off right and feeling accomplished and proud right from the start.
Make calendar/lists/kanban for yourself. This has been mentioned by others already so I won't harp on it too much. You can experiment and find what style works best for you. I use a personal Trello board and have it broken down into Backlog, Doing Today, Current Task, and Done. Each task is color-coded based on how hard/time consuming it is. When you finish a task and drag it over to Done, it feels good. Nice little dopamine burst. Dopamine bursts will keep you going.
Gameify your work. I take regular legally required breaks (2x 15mins and 1x 30min lunch) during my day but when I finish something or make significant progress, I reward myself. This doesn't work well for me if I do it based on time, because then I'm just clock watching, but if I do it based on amount of progress within a given task then I find I'll work a little harder and longer if I know I can go play Switch or read a book in the breakroom for 15 mins after hitting a milestone. It's all about that dopamine reward cycle, keep a carrot on the stick for yourself.
If you need to fidget, then fidget. If I am reading or sitting in a meeting I think best and retain information when I have something to do with my hands. There are lots of ways you can do this without being distracting to others. Twirl a pencil, get a fidget spinner (the quiet one) or a fidget cube (these are awesome), silly putty, legos, something like that. I have a set of building block looking things (they're actually surplus equipment from our lab, but they look kind of sort of like legos) I keep in our meeting room and every morning huddle I make a different pattern or building with them. (Don't make noise!) My boss is aware of my situation and 100% cool with it, and even though I might not look like I'm paying attention, when it's my turn to participate in the conversation I can perfectly repeat everything that was said up to that point and then give my part too. Ironically, if I was sitting there motionless and trying to pay attention, I'd probably be thinking about video games and dinner and not mentally engaged at all.
Take a step back, walk around. Closely related to fidgeting. If you're sitting there and just not accomplishing anything, go take a trip to the bathroom, water fountain, window, courtyard, whatever. Just get up and move for 5 mins. Having a change of scenery forces your brain to reset, and you're still thinking about things even when you're not thinking about things. I've solved a number of bugs while I was on the crapper.
Procrastinating can be a good thing. Got a complex task and you're having trouble staying focused? It's REAL easy for muscle memory to kick in and you open a new browser tab and now you're looking at cats on Reddit and before you know it it's been 20 mins and you don't even remember how you got off track. Don't do that. You may want to try a browser plugin like StayFocused in order to help you break the muscle memory. You can still disable it and go to Reddit like normal, but it can be nice to have a screen pop up and say "hey, you should be working!" and have it jolt you back to focus.
Here's the cool thing though: you can harness this. Don't want to work on your big hard task? That's fine, you can procrastinate into lateral productivity. Quit working on your big hard thing, and do something easy and short. Maybe the easy short thing isn't the priority you "should" be working on, but you can take a breather from whatever is daunting to you and still make 100% use of your time. Then when you finish your big scary thing, there's no more wounded soldier to finish off!
These have been game changers for me, some were tips I got from more experienced ADHD kids and some were trial and error on my part. Hope this helps. If I truly sat and wracked my brain a while I could probably come up with more, but I need to get back to work too. ;)
The last thing I'll mention, look up How To ADHD on Youtube, it's a great channel. (I can't link it, it gets flagged as spam for some reason...? >:( ) While you're on that channel you should look into making your own calming/focus jar, it's helpful for a quick mental reset and also makes a neat desk item conversation starter. :)
Bottom line: Once you get your arms around this, it's hard to view ADHD as a disability, it's more of a character attribute. Not good, not bad, you're just different. You have a different set of strengths and weaknesses than a neurotypical person. You can harness this. You need more structure and planning in your life, but you can work faster and more creatively, juggle many tasks, and approach problems in a manner different than most others will.
You have value and worth, your contributions matter and your organization would be missing out if they didn't have you on board. Never forget that.