Is this normal?

I don't know if it's normal, or if all pregnant women go through this. But hopefully someone can tell me. I have been experiencing some weird things, but only after sex. It's like a really sharp pain in my lower stomach and lower back, and then I start to feel like I am going to throw up, and have before, and then I get a blinding headache. I feel dizzy, and just horrible. I didn't know if it was serious enough to call my doctor, but it doesn't sound normal to me. Has this ever happened to any of you? At first I thought it was a coincidence that it happened right after sex, but then it happened again, and again. So I know that it has to be from that, but I don't really know why.