So many (((HUGS))). I agree with all of the PPs, that it sounds like the reflux isn't controlled, which means that APOP is a great means to get your LO to sleep. When I was in your shoes, I couldn't figure out what I was doing wrong and really it was just my LO was in so much pain, there was nothing I could do in regards to sleep training, until he was better.
I also think that 3 hour feeding is more appropriate at this age. Both of my LOs were big at birth and didn't move to 4 hours until they were 4 months.
Rantidine didn't work for either of my LOs and they needed a PPI like Prevacid.
Also, both of them have intolerances to milk and soy (MSPI), which caused reflux. Have you talked to your ped about this?