Мама двоих (3 года, 5 лет), ждёт третьего

Trouble with doppler at 11w after working well 8-10w?

I've been easily finding baby's HB with the doppler since 8.5 weeks. I think twice I couldn't find it, but most of the time I found it right away. I'm 11w now and the last two times I've tried it's SO hard to find! I did eventually find it, but it sounds like it's being muffled under some other sounds. I'm still bleeding on and off from the twin we lost, so I need the reassurance ?.