Sorry you feel that way, i hav to agree with what some have already said and would sugguest that you might try a fitting. I went from being flat to a full C so wearing a bra is required for the most part. After being fitted I find that most of the time I heardly know I am wearing one. I also agree that a sportsbra might also be something to consider even for everyday use there are a couple of site like Title Nine that could be worth a shot and maybe call for advice.
hope that helps