Baby moving at 20 weeks?

Okay, I'm overweight and I'm 20 weeks pregnant. I'm not sure if I feel my baby moving yet or not. I haven't felt the "erflies," but I have felt something. It feels like a twinge - kind of like a muscle spasm. I've felt it probably 10 times in the last couple of days. Once it was really low in my stomach, and I pushed it. Then I felt it again in the same spot. Is this my baby moving? Or is it just my belly feeling funny?