Right.......
Firstly it may be a little early to hear on a home doppler.
I tried for hours to find my babies heartbeat when doppler first arrived, in the end I did the following and found babies heartbeat in about 10 mins:
Firstly listen to your own heartbeat so you know what to expect - remember you can hear your heartbeat in a number of places - so you are looking for a beat similar to yours, but going at a much quicker rate
Make sure you use lots of gel - it makes a huge difference.
Place the doppler on your pubic bone, or just below your pubic hair line, right in the centre (if you drew a line down from your belly button).
Move the doppler literally a millimetre at a time and angle the doppler in different directions - you also need to press quite hard.
Start by moving slightly to the left and then if nothing move slightly to the right - VERY VERY slowly and keep ensuring you change the angle of the doppler.
If nothing try even lower down.........
You will be very surprised at how low you will find the heartbeat.
I started by moving it across my whole stomach and eventually found the heartbeat fairly central (a couple of cm's to the left) and half an inch below my pubic hair line......wasnt ever expecting to find it so low down
Any problems or questions feel free to ask or PM me if you prefer.
Lots of luck and you will find it eventually (I didnt get my doppler until I was 16 weeks though).
Where abouts should i be placing it to try and find beans heartbeat? 
