"Splitting" Feeling Above Belly Button?

I'm 25+4 today and several days ago (2), I started feeling this pain above my belly button. It's a moderately sharp, achy feeling like a bad bruise. A girl I work with who has a 3 month old (who's body is very small) said her muscle wall tore while she was pregnant and she had the same pain. I weigh 139 and I'm 5'6, only gained 13 pounds so far. Another girl I work with who has an 18-month-old baby said that it didn't happen to her but it's a more common thing with tinier waisted girls. Do you think that's what could be happening, my muscle starting to tear?