I third the UTI thing - pays to have it checked out just in case... they're best nipped in the bud than left till they get truely awful. I have a fantastic home remedy for mild UTI's, but sadly, it's not suitable for pregnant ladies! Alas!!! I mean, we're the most likely to need it!
Anyway, the sore, heavy belly thing sounds just like me these days, so mightn't be anything to worry about - the joys of being up the duff. I get tender because it's so blinkin' easy to strain a muscle round there. Up until recently I didn't really understand why pregnant women were constantly uncomfortable... NOW I'm getting an idea what that's about!!