Does it just feel hard? or does it feel like a constant tightening like a BH? If it feels like constant tightening, I'd probably ring the midwives and ask them, but otherwise I wouldn't worry.

I'm trying to think back to what my belly was like... LOL.. I think it felt pretty hard, and when I got BH's it morphed into wierd shapes hehe. And I remember with DD thinking there's no way my belly could get any bigger, it just felt so hard and stretched to its limit.