Doppler advice needed!

I've been using a home doppler for several weeks, but I've found the heartbeat in the same place since about 11 weeks. I'm now 16 weeks, and can only hear the heartbeat pretty low near the pubic line still. I have a nice sized baby bump already (second baby), so I would have thought baby would have moved up by now. Is this normal? How is baby so low still with this big bump?! Haha. The doctor told me I have a rear placed placenta, so I should feel the baby by now (but there has only been a little noticeable kicking), so maybe she was incorrect? This picture was taken at 15 weeks. Thanks for any ideas!