How to fix discolored teeth?

I have braces and i admit i USE to not take the best care of them. I brush every morning and most nights( sometime i fall asleep before i do). My teeth are not yellow, but they are discolored. my ortho gave me Pro Dent and i just recently started using it. How can I fix it? I dont wanna get a kit or anything and i cant wear the crest white strips obviously, help??