Sex while pregnant...

So the first 3-4 months of my pregnancy I wanted nothing to do with sex. My boyfriend would try and I wouldn't even want to be touched let alone cuddle at night. But right when I hit 4 1/2 months my labido shot through the roof! I wanted it everyday multiple times a day. My bf would joke he couldn't keep up anymore lol... It's been the same ever since then until recently I want it just as much but it's starting to hurt now...? What is up with that. It never hurt this whole time and now I can barely tolerate penetration. I am 31w1d today. Any thoughts?