Reflux

have you tried other formulas to make sure thats not whats upsetting his stomach?

If all the conservative measures aren’t helping I’d go ask your GP for gaviscon or omeprazole xx

That's usually dairy allergy. Try a dairy free formula.

And yeah it would have happened while breastfeeding, if you were eating dairy, because the dairy protein passes through the breastmilk

Gas drops and gripe water may help

My daughter took medicine for it for a while

My son was given omeprazole for the mornings but screamed after tasting it and would fight me when I tried giving it, so he got carobel thickening powder to add to all bottles/ give before feeds. Speak to the GP/HV and see if they would recommend it but it was a lifesaver for my little one!

We had this with my youngest (he’s now 11months) I didn’t want to go straight to Gaviscon so started with Carobel. That seemed to do the trick for us and now he’s on solids it’s so much better!

If breastfeeding he might be having an reaction to what ever you are eating an he reacting
If formula he could have milk allergy.
I tried everything an nothing worked except for the expensive nutramigen formula an I mixed it with some of my milk, we seen an ent, gastroenterologist an they found no issues or concerns they did say to try gripe water we did definitely didn't work
Finally when mine hit 13m we stopped an went to real food an no issues since

I think mine just hated formula an milk altogether
Mine was 27+1 even in NICU she had a difficult time drinking on her own she was on ng tube. When we brought her home the same setup had a nurse that did the machine for me. When she left an didn't visit a week later I told her my child vomit after each feeding that when we went to gravity. We switched thru our provider gravity feed an it was less of issue but after so long they wanted to see why the ENT couldn't find any issues gastro wanted to push into stomach feed surgery I said no unless they found an issue.
You can try changing bottles. I bought every single bottle an every single special nipple so far Mam bottles worked an nutramigen worked the most once I started adding less formula an more milk it was complete game changer. You can try at 8m I think regular an go from their mine did start at 6m slowly an around 10month is when we slowly made the change an 13month is when I switched to baby food an no formula

if you really want advice its hipp antireflux milk give it 2/3 weeks to start noticing a significant difference. my daughter was the exact same it was horrible and the doctors werent doing much because she was gaining weight. hipp antireflux is hard to find (only in boots) but you can order it. it is the only thing that helped and my daughter was on gaviscon and omeprazole and both didnt do as much as hipp did.