Irregular fetal heartbeat?

I'm 30 weeks pregnant with my second child. I went to my ob yesterday and when he went to listen to his heartbeat, it kept skipping beats consistently...he said it's probably nothing but he ordered an 'urgent' u/s. It's not for another two weeks so I'm going crazy worrying. And now I'm noticing today he hasn't moved around as much as usual...on a normal day he kicks, punches and rolls like crazy. He's still definetly moving but they aren't as strong as usual which is making me worry even more! Am I just being overly paranoid? Has anyone else had this happen? My daughter is 5 now so I don't recall if her movements slowed any at this point. Any input would be great! Thanks.