That's how I was at 9 weeks. I would find the heartbeat and then I couldn't find it again. I would then take a break, come back to it in a couple of hours and then I could find it again, although it sometimes took 30 minutes! Now since I am further along, and I know where the baby hangs out, I can find it right away. I had a sonogram a couple of days ago and heard the heartbeat and I said to myself, "wow, that is the same heartbeat that I hear on my doppler at home all the time"! It was a good feeling to know that I was hearing the right heartbeat, and not my own or any of the other weird noises at home!