What’s wrong with me?!?!

My period is never right on time but it usually shows up within a few days. This month it was 2 weeks late. I took a pregnancy test the day after it was due and it was negative. Finally started yesterday and I was folded over on the couch in pain for a lot of the day. Terrible cramps and such heavy bleeding. My son was born almost a year ago and that’s the only other time I remember bleeding this much/this big of blood clots. If it wasn’t for the negative test I would think I was having a miscarriage. I feel like my uterus is trying to fall out of me.