Didn't get to hear the heartbeat (but don't panic)

Well, I had my April pre-natal appointment yesterday. I'm 13 weeks, so I was *supposed* to get to hear the heartbeat yesterday. I know it is sometimes difficult to find, but I was also in a mild panic because all of my pregnancy symptoms seem to be going away (except the sore chest) and I had been having minor abdominal pains off and on for about a week. So when she couldn't find a heartbeat, I did get concerned. "There's no one in the ultrasound room, let's pop over there and have a look-see, shall we?" Fine with me. At least it was abdominal this time. Still couldn't hear or see the heartbeat. Why? Because the baby wouldn't hold still long enough! S/he was just wiggling all over the place the entire time (no, I can't feel it yet). We could catch glimpses of the heart now and then, but no steady view. The doctor's comment: "Well, generally if they're moving like that, they have a heart, so don't worry about it. We'll catch it next time when we do your major ultrasound." I didn't think I would be having "the ultrasound" until June (21 weeks), but she said that she thinks next time will be fine to check on major feature development (17 weeks), particularly since I do not want to know the baby's gender. So I should have new ultrasound pictures to share next month. Yay!