Hi Nicole,
It could possibly be your sacroiliac joint that has become slightly inflamed. I aggravated this at work when moving stock around, and my Dr told me that it is actually more common in pregnant women because everything loosens up and moves in preparation for carrying a child. If you Google it, it will describe the pain you are getting pretty much exactly. The best way to alleviate it is with a heat pack and when you are sitting - place a firm pillow behind your back for support (including when driving), you'll need to limit bending and twisting and make sure not to lift anything heavy.