The dopplers that the Drs have can generally hear from 10wks or so it wouldn't hurt to give them a call if you really are worried. At least it may ease your anxiety! If you were closer to me I'd say come on over and try mine! Dont be alarmed though if they cant hear it you may just need to wait a little while longer. Another option is to go to the maternity ward of the hospital you'll be attending and ask them to check on their machines. They'll pick it up no trouble with the equipment:-)
And with your ticker you'll need to copy & paste one of the other options they give you...then it should work. Just preview it til you see the picture:-)