i have a doppler.....and use it less and less....as mentioned above when you notice fetal movement daily you tend to lean more on that than the doppler. I probably check it once a week now. And I cant always find it...... all the more reason I worry less if I noticed movement. Im sure you are fine....but try not to stress. :-)
Do not worry about not finding h/b. When I got my doppler (at 11 weeks) I managed to find h/b right away. I was soooo excited! Then 5 min later I wanted to hear it again but could not find it no matter how hard I looked. I hear it will be easier to locate as your baby grows and you will not have to press as hard.
Good luck!
I have used a home doppler for my last two pregnancies. It is true that you shouldn't over use it. They don't know what affect it has on the baby. It is also true you shouldn't be too upset. What that doppler is doing is echoing off of the actual heart beat to produce the sound. It is not known how that sound affects the baby. When I use it now at almost 34 weeks my son kicks at it like, "hey, mom..turn it off". Early on when I would try to find a heart beat I would watch where the dr would go right to it and try starting in that area. If I didnt find a heart beat right away I would stop and try again later. It gets you more upset than anything when you try and can't find it. I am sure it is all ok but don't worry about it so much. Try to relax and lay on your left side if you are far enough along to feel the baby moving. :)
Helen72 is using a doppler, so perhaps she could offer you some advice :-)
Melimeli's right - I wouldnt worry about it either. Although I have read that they are not good to use more than two or three times a day, I know that when I went for my 19 week ultrasound it went for a good 45 mins and ultrasound machines use much higher frequency waves than a doppler. I do have a doppler but I only used it once a week or so - once you start feeling the baby move you might find like I did that you wont even have to use it anymore because just feeling the baby move is reasurance enough.
I wouldn't worry too much... I used one with my last two girls and used it everyday... worrying about it will do more harm to the baby than the doppler... stress isn't good... you will be fine... good luck