Painful sex....

So I'm in my third trimester and I only have about 7 weeks left till I deliver. My husband and I have been having sex successfully throughout my entire pregnancy and haven't had a problem so far. Until last night. It was so painful that I cried. He felt so terrible and started crying too because he thought it was his fault. It was the weirdest feeling. Of course I will be telling my doctor about this next week when I go in for my next appointment, but I wanted to know if anyone else has felt pain when trying to have sex far in your pregnancy.