I have PCOS & I Think I'm Pregnant?

Okay so i'm 17 years old && I think I might be pregnant . I have PCOS ( Polycystic Ovarian Syndrome) so i don't get normal periods. i've only had two in my whole life and that was in April & May of 2011 but the only reason i got them was because my gyno put me on birth control too regulate my period. well my mom never got my BC refilled so i stopped taking it && therefore i stopped getting my period again . I keep having all these signs of pregnancy (sore breasts, back pain, headaches, nausea) & i've taken 4 HPT & even got one done at a clinic but they all said negative. one of my friends has PCOS as well and she said she had too take 10 test before the last one showed up positive. i'm just kinda freaking out and i dont know what to do. the scariest part though is i keep getting this like brownish discharge and i looked it up and it said it might be implantation bleeeding? but yesterday i stood up and all this blood just kinda came out so i put in a tampon & later that day i put in a fresh one before work and after work it was still completely white!? but the same thing happend today too. i was at my friends and i went too the bathroom and all of a sudden a big amount of blood came out but when i got home it stopped? i have no idea whats going on and it's freaking me out. me & my bf kinda think i had a miscarriage but i'm not for sure so i dont know what to do . does anyone know what could be going on? please && thanks!!