Formula intolerance is much less common than most people think. Lactose intolerance virtually never occurs during infancy. A possible problem with formula at this age would be a milk protein allergy, which isn’t common and usually goes along with rashes, eczema and failure to gain weight.
Two other explanations to consider are reflux and gas. If your baby is a “gulper,” eating quickly and drawing in air during the process, he may be getting bloated and uncomfortable with feeds. In this case, slowing him down or changing to a different bottle system and frequent burping may help.
Reflux, in addition to causing spitting, can cause an “acid burn” in the esophagus and pain during eating. Babies who have this problem are very uncomfortable during feeds, often arching backwards. Simple changes such as keeping a baby upright for 30 minutes after a feed usually help, as can medicine if necessary.
If your son continues to be uncomfortable, talk to your pediatrician about these possibilities.