Intolerant / bowel movement babies.

Hi everyone, so my son (8 months) has always had problems with formula and milk. First 2 weeks I had to exclusively formula feed (aptamil) as I was having to be on strong pain relief and he was constipated. The doctors said this was normal so I went into breast feeding but he was wanting to feed every 30 minutes and was still constipated and they gave him a laxative, this relived the constipation but still feeding every 30 minutes. At 9 weeks I put him back on formula thinking that maybe he needed hungrier baby. So until he was 6 months he was on cow and gate hungrier baby stage one and was doing better. No laxative but this is where we had the opposite effect. His poos became acidic and was burning his bum straight away and he was bleeding and peeling. We was changing him straight away before he had even finished (he likes to poo when you’ve taken the nappy off and always has). We have tried all different creams even some prescribed by the doctors and I’ve changed his milk after 6 months which is when it’s started to get worse. I’ve tried in total aptimil stage 1 & 2, cow and gate stage 1 & hungrier baby, sma stage 2, kendamil stage 2 and in the goat milk, nutramigen stage 2 and nutramigen puramino. All of these have caused him to have stomach ache and poos that burn him but he is not vomiting up any milk. At the moment I have put him on oat milk and he isn’t having acidic poos and I’ve completely took him off all lactose. I make all his own foods so I can completely cut out milk and even use substitutes. At one point I even took him off food and just gave him milk. The doctor is unsure now and is saying they don’t think it’s a milk allergy as he has had the nutramigen prescribed. I’m just looking for anyone with a similar situation?