What is this?

I started feeling bad again in the afternoon...had to lie on my side, with as few ups and downs as possible (to feed the kids) until Tom came home. Then when I got to lie down for 20 minutes, I felt better so we went to swim lessons. I will probably call the OB nurse in the morning, but I think I'm probably just experiencing different hormones, in addition to the baby sitting on something that wasn't meant to be sat upon.