Fetal movement doesn't normalize until about 27 weeks. At this point the baby is still small enough to find places to hide. When I was 20 weeks I went to the hospital because although I had been feeling strong movement since about 17 weeks it had completely stopped and I hadn't felt anything for 3 days. They found the heartbeat and then gave me an ultrasound and there was my little bean just kicking away but because of the position she was in I couldn't feel it at all.
As the baby gets bigger, what doctors say to worry about is when you don't feel the baby move for an extended period of time. I'm pretty sure you'll be okay, but if it makes you feel better, go ahead and call your doctor. Hope everything's well!
I'd call your doctor when you get a chance because I believe that you should report any decreased fetal movement...it is probably nothing to be worried about but I 'd let the doctor know just to be safe.