help! what do you think? (maybe TMI?)

Hi everybody! I was supposed to get my period 2 weeks ago and it never really came. I just had two tiny blood clots, and when I say tiny, I mean REALLY small. It is very off for me. I am sexually active, but I'm on the pill and we are always safe about it. I tested anyway to ease my mind and it came out negative every time, but something doesn't feel right. I recently started college and have been under a lot of stress. I never take the sugar pills in my packet either, I know that there is always a possiblility, but it is freaking out. Can anybody give me any advice or input? Thank you.