Could this be anything other then baby movement?

I'm 18 weeks pregnant and in my lowest part of my abdomen i feel little movements that are getting increasingly more powerful as the weeks go on. I know this is the point when some girls feel the baby. But i'm just wondering if at 18 weeks that the baby would be in the same spot as it was at 15 weeks in the lowest part of the abdomen . The feeling feels like one random pound on the inside of my stomach. It doesn't feel like butterflies or fluttering. Its just alittle pound and it stops. I don't thinks gas b/c my stomach feels calm right now.. If its not the baby what else could it be?