Dont know whats wrong with me!please help!!!?

I am currently on my menstrual cycle and I've had really bad lightenedness and I've fainted 3 times. I was at the store and had to crouch and put my head between my knees. I feel really weak. No pain or cramps but when I got home and sat on the toilet globs and globs of blood came out. I am on the pill and have been for almost 5 months. I was tested for anemia and all that a year ago and my hemoglobin and iron was all normal. I do tend to have lower blood pressure , I'm skinny. I'm worried cuz I've never bled this much and its still continuing as a heavy period. Please help!!!