As Emma said sex if perfectly normal during pregnancy. You only need to avoid it if your ob/dr/mw said you should avoid it. I had a case of bleeding from the cervix early on after we had sex but we just needed to avoid it for 2 weeks until I healed and everything was fine after that.

As for sneezing, I was careful not to sneeze too hard just for my own peace of mind but I don't think it does anything either.

Both of these things are normal. I hope this helps.