I have been in a similar situation in the past. I made an internal transfer and then regretted in a few months later, and started looking for another position within the company
First thing you have to do is to quietly investigate the procedure for applying for internal positions. I have worked for companies that required an employee to stay in a position for 6 months or even a year. Check the intranet for an employee handbook, check the things you were given on the first day. You could also start to try and apply for a position to see if it stops you, but don't complete the request. One place I worked for would block your attempt in the job posting system to apply until you has met the minimum time in position after being hired or transferred.
Check your paperwork to see if even a transfer would jeopardize any hiring bonus, or moving expenses reimbursement or if you would have to pay them back for training you received. If your current position is hard to fill a bonus might have been used to attract candidates, and they don't want to shell out money every few months.
Since you are new hire check to see if there is a probationary period. If you are in that period, then applying for another position could make your current boss decide to exercise his right to terminate you employment.
So should I apply internally, or will I look like a complete high
maintenance jerk for looking for something else after only a few
months because the current job is boring?
So assuming you can apply, and there is no risk in applying, and you won't owe the company money if you transfer, there is still one problem. Many projects would be reluctant to hire you.
If you are still in a probationary period, they may believe that your manager is trying to get rid of a poor employee without having to fire you. One manager at a place I worked made it clear that they would never even interview a current employee trying to transfer who was switching jobs after less than a year. They felt that they were looking at either a person who couldn't commit or somebody that wasn't a good employee.
Can I tell an internal interviewer that proofreading other people's
code is not what I'm looking for in a job, in other words, the job
just wasn't what I expected and I'm more excited about the job they're
Yes. If you get to any of the interview stages (phone, in person/video...) expect they will ask why you are switching. Just remember how they weigh your answer and your honesty is unknown. They can decide that you will be bored with their job, and reject you; or they could say good answer and keep you in the process.
So should I apply internally?
But also apply externally. Because once your current manager is told you are looking elsewhere your days on their project could be numbered.