HIPP Anti Reflux Milk

My 7 week old baby started showing signs of reflux around 4 weeks old, I tried everything natural to help (sitting up right, pace feeding, even changed teats to different brands I’d heard were good with reflux) nothing worked. Went to GP and was prescribed Gaviscon which after a week did nothing except give him slight constipation. We had discussed a possibility of milk allergies how ever he had never had any rashes or diarrhoea, so we tried him on HIPP anti reflux (I was using this brand before). It helped instantly and was such a relief (for us both) that he could comfortably drink his bottle without any back arching and crying out in pain. After 24 hours I noticed his poops had changed to more of a looser, frothier consistency (somewhat resembling the milk) and just thought it was due to his tummy adjusting as it did say this could possibly happen (that or slight constipation) but as the reflux was being treated well I wanted to see it through. We got to day 5 and his poops had got looser, completely liquid and still frothy, bright yellow with no smell and exploding out of almost every nappy. I was concerned this was diarrhoea so we and to a&e as I didn’t want him to be dehydrated and he was sleeping quite a bit and not drinking as much as usual. They said he was fine and that they believed he has a viral infection coming on (snotty nose and slight cough) and that the poops could be to do with this. Slight coincidence it happened 24 hours after changing milk? Who knows.. He has no temp, no smell or blood in poop, he’s still gaining weight and isn’t dehydrated so shall I continue as we are? His bum was quite sore so we’ve used metanium which has helped and just keep letting him get some air in between nappy changes. We have another GP apt today but I thought I’d ask for advice incase anyone on here has experienced the same or similar reactions? We did try to change him back to normal formula with the gaviscon but he wouldn’t drink more than 10mls without screaming, choking and refusing the bottle.