Baby?

How exactly do you tell if you've started to feel the baby? For the past 4 or 5 days I've noticed a sort of thumping sensation. But with my digestive issues, it could SO be some lower GI thing despite the fact that I haven't had any problems in that department. If I had to describe it, I'd say it feels exactly like a random intestinal blip. It's just happening a lot more often and isn't associated with any bathroom emergencies. So is it the baby?