What does baby movements feel like?

I'm 18 weeks pregnant and lately i've been feeling little pounds in my lower abdomen. I'm unsure on if is the baby or if its gas bubbles or ligaments stretching in a painless way, its so low and always thought that the baby is higher in the abdomen at this point? Has anyone ever experienced this and found out what it is?
Maybe its not the baby.. i feel nothing down there when i sit.. Just little pounding like right now.. but when the pounding goes away i feel nothing!