I'm not completely sure if it is normal or not. It could be what was happening to me at the end of my pregnancy. Sex was okay unless he put it in to far and then I would get a pain something like what you are describing. Could that be what is happening to you?

I get that same pain, I am 31 weeks, if we are having sex in an ackward position, and if my daughter is moved down, putting pressure.I asked my doctor about it at my last visit, and he said to just be careful while having sex, nothing to rough, and to just use caution. You may want to ask your doctor because everyone is different, but that was what worked for me.