Is it safe to have sex in third trimester?

Hello everyone, is it safe to have sex while 36 weeks pregnant and baby is really low?
Also I have been having cramps and her movements are very low in my pelvis. 
Should I avoid altogether? 
I will be measured tommorow by my OBGYN
(By the way what do they do in that appointment??! And what to expect☺️?) 
Just curious and wondering