Two different fetal doppler rates

So having a history of miscarriages. I like having a doppler to comfort me once in a while to remind me everything is ok. I've had 2 ultrasounds so far. 1st on was transvaginal only and they got 1 with good heart rate at 6 weeks 5 days. 2nd ultrasound 5 days later on abdominal immediately showed twins with visible heartbeats but when they did transvaginal she couldn't get proper measurements and said she wasn't very familiar with multiples. I have another one next Tuesday at 10 wks 4 days for my Dr to confirm the twins and get proper measurements. Of course I'm scared tho, lol. I was using my doppler earlier tonight and I usually can only find one heartbeat located on right side of belly button near pubic line. Tonight I couldn't find it right away in the usual spot so I looked for the other ones beat. I picked up 180bpm on opposite side than usual. About 20 min later I tried on the usual area again and got 162 bpm. Do you think I finally picked both up tonight? I can't imagine heart rate could drop that low or be on opposite sides like that.