Acid reflux babies, a sleep question?

Does your little one sleep on their tummy? I have heard so many times that this is the most comfortable for them. Sophie is 5 months old and takes Zantac twice a day. She seems content except at bedtime. She keeps waking up grunting and kicking her legs out, locking them at the knees. She cries and fusses. I've tried everything: gas drops/tylenol/gripe water/pumping her legs/and even nursing her. The only thing that stops her crying is for me to roll her onto her stomach. She farts really loud and goes to sleep instantly. So, I try to roll her back over and she wakes up grunting and crying in like 5 minutes. I put her back on her stomach and out she goes. She has done this for 4 days in a row now. I didn't get a wink of sleep last night because I had to keep checking on her to make sure she was breathing ( I know her neck muscles are strong enough now and she pushes up a little with her hands too, but I'm still paranoid!). Her MD said soon enough she will be rolling over and I couldn't stop her from sleeping on her stomach. I'm just scared. She sleeps soooooo well on her stomach though. She doesn't wake up once for about 10 hours, not even when her pacifier falls out! Advice????? Thanks!