Plus size momma and fetal Doppler

Alright I have an at home fetal Doppler. I am plus size. I have been trying to use it for a few weeks now and am not able to find the heartbeat. I’m 15 weeks and 4 days. Anybody have any recommendations. I have had doctors appts and ultrasounds. And at the last baby appt they had to send me for an ultrasound because they had issues finding it with their Doppler also. It was confirmed with ultrasound. Just trying to find some tips and tricks to using this Doppler.