Is it the baby?

I'm about 15 weeks and a couple of days ago I started feeling this weird feeling on the left side of my belly about mid way. At first I felt it when I stood up, almost like a delayed stretching feeling. Then I started feeling it when I was sitting and not moving. It's almost like a slight pressure or maybe a type of vibration or something. It occurs in the same spot every time for only a few seconds at a time. It doesn't hurt or anything. Its now been 3 days that it occurs off and on all day. Sometimes when I'm sitting and sometimes when I'm moving around. Could this be the baby? I only doubt it because it seems like it's too high on my belly. I imagine the baby is still low in my abdomen. I don't know what else it could be though. Never felt anything like it. Any ideas? I'm beginning to wonder if I'm crazy. (Obviously this is my first pregnancy). I just don't know what to think.