It only happens with formula? Does he vomit after any solids?
@Samantha no it’s only with formula even before starting solids
It just seems odd that he would be allergic to formula and not to any solids. Has he had cows milk or other things with cows milk protein, like cheese or yogurt? I'm sure you're right that it's something, but an allergy that is inconsistent is strange. Could it be that he has acid reflux which would cause liquid to come up but not solids? Does he drink water? I mean, we're not doctors here so it's hard for anyone to say, but it's probably worth a second opinion from a different doctor. My son vomited a lot after eating and it truly wasn't a concern in the end. You're also close to him fully transitioning to solids!
@Samantha actually he doesn’t do well with yogurt either, it gives him eczema
Dairy gives me eczema too, but only when I'm pregnant! Honestly it is really hard for a layperson to guess what's going on. Based on what you've said, I would keep pushing for an answer and test what you can on your own - switch to a dairy free formula to see what happens or try a slower flow nipple or pace feeding just in case it is acid reflux.
You could try something non-dairy, like Nutramigen, to see if that makes a difference. A sensitivity or allergy to cows milk protien would be the most common cause of something like that. Unless the vomit is projectile or high volume most Drs aren't concerned, unfortunately