My OB used to have to get me to drink iced water and then retry. DD was such a lazy bub in the early days and would tuck herself as far back as possible making it hard to find the HB. Until about 20 weeks I ended up taking a bottle of water with ice in to drink pre appointment in the waiting room so DD would start wiggling. After 20 weeksish DD would flip all over the place and kick the doppler

I wouldn't worry, it's a common thing for dopplers