What Causes Slight Bloating In Abdomen And Cramping?

I was 3 months pregnant and miscarried. After a few weeks if bleeding I stopped and then had my normal period. Well, it was heavier but was for my normal 5 days. I then started bleeding again 3 days later but it was almost black and not heavy. Enough that I needed tampon though. It has been a week so far of dark and bright bleeding that also stops and starts. But now I have slight bloating or swelling in abdomen and now have cramping or heavy abdomen feeling.