Ellie whilst some people can find a heartbeat via doppler prior to 16 weeks these are exceptions and not the rule. As you know your baby is tiny - it is usually lots of persistence or luck that can locate the fetal heartbeat via doppler this early.

I wouldn't even try at your gestation - it is stressful for the mother and the operator and also unlikely - as I said with persistence and a good dose of luck it is possible to find it but the time it takes causes undue distress (imo).