I think your belly is just fine. You look like you're quite small when not pg, I imagine your tummy was nice and tight? Some people don't pop until 20 or so weeks, I bet you find you will pop out all of a sudden and you'll wonder how on earth you got so big so quick. The best thing to do is IGNORE EVERYONE'S comments when you are pg, no one says anything nice or constructive at all, so put try to ignore things like this.

Not too sure about your pain, possibly it's just your belly stretching?