D.K.
Sorry but your Dr's advice doesn't seem okay with me. That is insane, tough love on a 5 month old?? that is a new one on me! I am all for not jumping with every fuss but not until later. At five mos they are wired to wake if they need something.
My daughter had reflux, she outgrew it by 6 mos, but if they have an empty stomach that esculates the reflux, did your Dr tell you that? Maybe increase the ounces at the feedings?? If he takes more then he needed more. Also don't assume the meds will work, if you are nursing he could be having a reaction to something you are eating too. Some meds work on babies and some don't. For my daughter it helped but at the same time it didn't totally go away until she just outgrew it and moved onto solids.
Also he could still be uncomfortable from reflux and going through teething, growth spurts all of which cause sleep disruption. At 5 mos if he wakes there is very well a good reason.
My daughter didn't go without a night feeding until 11 months of age, my son didn't sleep all night until 10 months!
At 5 mos he is growing fast, brain developing and they know when they are hungry and you did not train him to wake.
I NEVER did cry it out until after the year mark and rarely had to do it after that other then teething and bad dreams or them being sick.