Home Fetal Heart Doppler

I recently got a home Doppler and after I used it the first time I started bleeding. I skipped a day and listened to it two days later and the bleeding started again. I've had bleeding throughout my pregnancy and the doctor hasn't been alarmed by it or anything because he said some women do bleed in the first trimester, but I'm just worried that the Doppler is hurting the baby. I read online where some doctors don't recommend using one because it sends waves through that hits the baby and could cause miscarriage in the first trimester. I mean, I know the baby is okay because I heard its strong heartbeat both times, but I'm scared to use it again. Has anyone else had this problem?