Pregnancy is awful, I know exactly how you feel Sazzy.
As for the rash, it could be PUPPP. I had that with Lydia and Alex (worse with Lydia), and it was horrific. I used to sit in freezing cold baths of water just to ease the itching. Eventually (near the END of the pregnancy, which is typical!) I managed to get prescribed some tablets but I don't know what they were - not sure if they were some sort of antihistamine or something.
Not sure if that's what you've got though because mine was all over my arms and legs and bump, but not above my bum.
If it gets worse though get it checked out.