J.H.
Hi Jamie,
Wow.... your third kid -- Congratulations! I'm actually a first time "mom to be" -- about 6 and a half months pregnant. I didn't really start feeling my baby kicking until he or she was about 20 weeks. Supposedly the placentia was placed "like a canopy" over the top of my stomach, and acted as a cushion between my baby's kicking and me. So that could easily be what's happening to you. If the movement is strong on the ultrasound, and it has a regular heartbeat, I bet your baby's doing just fine.
Take care,
J.