Guess my question would be is there anything else I can do to have my salary up to the level's minimum? I don't think in the legal sense there is anything (back pay, etc..) but it just seems a little unethical to me
You should handle this situation like any other raise negotiation; You tell your manager that you want an interview to discuss your salary. You explain that you have gained achievements y and you've reflected experience x at work and that you wish to receive a raise of z% which is u% from the market's average, based on a research which you should always do before a interview as such.
There's nothing unethical about you having a lower salary than someone else since you haven't requested a raise before; you wouldn't find it unethical for someone else to have a lower salary than you if that individual never asked for a higher salary.
Don't concentrate too much on your coworkers, focus on your skills and use them to get the raise you're looking for, just remember that you have to ask for it, no one is going to give you a raise just because.
