fetal doppler 10/11 weeks

To those of you that have used the sonoline b around 10/11 weeks (I'm currently 10+5) did you ever find the heartbeat really strong and then struggle to find it again? 
At my 8 week appointment I was told the baby was really far back. And on 10 weeks exactly I was able to find the heartbeat at home. But I haven't really been able to since then. Just wondering if anyone else has some tips/tricks or advice.