There will be months that you will not feel as much movement. Reason, space is limited in there. As long as there's a heartbeat and the baby is growing well according to the ultrasound, everything's fine.
Are you getting your kick count everyday? Lack of movement as they get bigger is normal..As long as you are growing like your suppossed to and getting your count and the heart rate is good I would say your ok...If you are concerened you can always tell your dr and they will give a stress test to check you out...Good luck..