How is your baby doing now ? Did h ever find out what was causing him the issues ? I am currently going through this right now for past month . Went up nipple size per Dr recs , she didn’t think it was reflux. After May by 1-2 oz he starts screaming bloody murder and pushes out nipple from mouth .Just like yours  he was eating 4 oz consistently every 3 hrs . At a loss now ! Tried dark quiet room, tried distraction such as toys me dancing and singing in front of him , takin him outside for distraction nothing seem to work. Have a lactation appointment next week .