What Causes Heavy Bleeding During Menstruation?

hi. i need help. i started my period yesterday but also started workin out and eattin alot healthier then. I woke up this morning with alot of blood clots, then i let it go, but i worked out, and took a shower, sitting on the toliet there was 5 more large blood clots, a lil bit more pain than normal, and heavy bright red blood. that hasnt happened before when i have exercised during my period. i have been drinking lots of water too, but for the past 2 days ive been taking lipozene to help me loose wieght and then 2 midols last night before i went to bed. i had protected sex with my boyfriend on feb 2nd only this month and i dont know what to do. what do u think could be wrong?