I get this quite regularly. I dont think it is anything to worry about, but if you are worried then go and get it checked it. I get it quite a lot after sex, I think that it is perhaps becasue eveything is so muchmore tender.
I think it's quite normal too. I'm sure I've seen something about it on another thread and loads of people were saying they'd had the same thing...especially after sex. On the few occasions I've managed to do the deed during pregnancy I've definitely felt a bit swollen and bruised afterwards.
I think it's just all the extra pressure from the weight of the baby as well as extra blood pumping round etc.
Probably extra pressure but if you are worried then speak to your MW.
Mine are very swollen and also a bit lumpy in places, sometimes they throb and are often a bit achy after sex. MW didn't seem overly worried, told me probably mixture of pressure and VVs and to get some support pants...