okay so i'm 15 and havn't had sex with anyone since end of December/ early January. not sure. and my period was last time 2 weeks ago but i have been getting really dark, gross,thick discharge.. disgusting i know. but idk wat it could be? also im on birth control so idk if that has anything to do with it? i have yaz. but i know i'm not pregnant cause i havn't had sex after my last period.. could this be a disease or std or something? im freaking out. but i've only had sex with 5 people. help?