Sonoline B baby doppler

So, I bought a baby doppler (heart monitor) on ebay the other day, I figured it would give me peace of mine between doctors appointments. Everything you read about them online gives you mixed opinions, either a. it's the best thing ever or b. it's a stress inducing noise machine. So anyways, I received my doppler this morning and was eager to try it out, after searching and searching we found what we believe to be the babys heartbeat, the bpm on the screen are reading in the 160s.... so a few hours later I go searching again for the heartbeat and nothing but my own... this continues off and on for the last 3 hours and needless to say, I am now stressed. I'm going to leave it alone for a while some people say you need to wait until you are further along. Now I'm just going to pray and keep my fingers crossed that Baby Lennon is hanging in there and nothing is wrong!