My son is 16 months old. I used to mix cow milk with his formula (about 1/6 would be formula and the rest would be whole milk.)

Recently I switched to giving him only whole milk (no formula.)

He throws up his milk now about once a week, something he didn’t do when I was mixing formula and whole milk.

My question is: could switching to whole milk only cause my son to throw up?

Or does this sound like more of a general reflux issue?