Ange, I was going to say it definately sounds like a hernia. My girlfriend had one during her second prg (her second twin prg i should add) and that's exactly what hers was like, very painful to touch.

She's had her babies now and i'm not sure that anything more has been done about it, but I've seen her belly and it looks like it's popped back in after the birth so probably nothing needs to be done about it now. She won't be having any more babies (hello, she has 4 under 3!) but if she were I'd say it would probably pop back out again.