They are growing pains. It's your uterus starting to stretch. It will happen all through pregnancy. They call it round ligament pain. I had it with DD around 5 weeks so bad I called the OB the next day. I seriously felt like I tore something in there. Everything was fine though. I had it through that whole pregnancy. Good luck.
I've been having those too, and I was told not to worry because it's just your body adjusting to having a baby inside of it! :)