I started feeling it around 16-18 weeks, felt like popcorn popping in my lower abdomen. Your uterus shouldn't be over your belly button yet (or so the books say) so any movement you feel down there could be it! I'm 23 weeks now and it's very obvious when he moves around so you're getting very close to knowing for sure! :)
Possibly every women is different as is every pregnancy I started feeling movement around 18 weeks