Can anyone tell me what's going on?

I started yesterday..it was my 5th day being late..last night I was sitting down and got up and I got really dizzy..then I started having hot flashes..and got dizzy again. I went and used the bathroom and seen that I started it was really lite. I have been having a pain in the left of my lower abdomen and when I was at work I seen clumps in my blood and it was a lot heavier..this has only happened once before and it was right after I started getting depo (7years ago for 1 year). I am not using any kinda birth control. I also have had diarrhea all day. Can anyone tell me what's going on?