I've heard that when you get closer to the due date the baby moves less because it's in position to be born and there's not much room for the baby to move around in the womb. This has happened to many of my friends. One even went to the doctor every day for the last 2 weeks before the baby was born. He was fine when he came out. If the ER said everything was perfect then I wouldn't worry about it.
Are they telling you what position your baby is in?? There is a post a little bit down and a woman's baby's back is up, so if your baby is facing your back, your spine will take alot of the blow, and you will be less suceptible to feeling it. Do not worry, if the u/s said everything is fine, then I'm sure it is. Drink some oj, or ice cold water, and try to stimulate the baby a bit, and count movements. I believe njeosys said in that post I mentioned that as long as you feel 10 movements an hour, you should be fine. Read that post, and please do not worry. It's not healthy for you or your baby!! Good luck!!