Thick brown vaginal discharge?

Okay, so I'm a female obviously, fifteen years old, on birth control, moderately stressed, and sexually active. A couple of months ago I changed birth control. For the first few months everything was alright, but recently I've been experiencing brown discharge through the entire month except when having my period. The texture varies from thin, light, and watery to very thick, and dark. There is no odor to it and I'm not experiencing any itching or burning. I'm fairly confident that it isn't an STD. I deal with it almost every day, but whenever it stops it's white and healthy. But that only usually lasts for a day. As you can imagine, this is very frustrating and puts a huge damper on my sex life. Does anyone know what this could possibly be and what I could do about it? I've spent countless hours looking for an answer, so any help is much appreciated. Thanks!