Not sure what's going on

I had a normal period right before Thanksgiving, and then completely skipped my next period. During that time though, I woke up about 2 nights in the middle of the night and would feel like I was gonna throw up. Last week I noticed my lower abdomen was feeling tight and without pushing very hard I could feel what feels like muscles and a general hard feeling. I took a pregnancy test and it came back negative, and then I started what I thought was my period that had severe cramps and feeling of nausea. The bleeding was very light, and lasted for about 3 days compared to my usual 5. Nearly a week later my abdomen area down to my uterus area feels hard like I'm flexing. I'm not sure what's going on and was wondering if anyone else experienced these symptoms.