I recently switched my 3 month old supplementation formula from liquid (enfamil neuropro gentlease) to enfamil (gentlease enspire powder) but he keeps spitting out when he burps. how do i know if its a milk allergy or if he doesnt tolerate it?

A test for milk and soy allergy is available by lab testing/ If the liquid formula was better tolerated, then the powder form preparation may have altered the concentration. Frequent spit ups and burping are often a sign of GERD which is common at this age. Reflux precautions include thickening the formula and feeding at a 30-45 angle. Watch for signs of vomiting, green tinge and follow up w Peds

True milk allergy is rare & symptoms profound, To me minor burp/spitting is what many do as they learn to feed effectively/deal with the common reflux. If it doesn't bother the kid, I would not keep switching formulas to find a magic one. as likely there is none. As they get past 6 mo and sit more the spitting frequency declines.