My 3 week old who is only breastfed often has gas, hiccups and uncomfortability an hour after fed, & dirty diaper every feeding. he did have 1 bottle of formula early and mom was on antibiotics. could his microbiome be disrupted from that? or normal?

The symptoms suggest your baby ingest too much air with breastfeeding; mom has to learn how to breastfeed and baby needs to burp after the feeding. It is less likely her loose stool is due to altered gut microbiome. The bowel movement could be due to quick feeding which is usually associated with too much air ingestion. The formula is less likely the cause if given long before the bowel movement.

Place baby upright on a burp cloth and a shoulder or seated on your lap and rub the back gently. A breastfed baby is also sharing mom's bacteria and should be quite well. Look for appropriate weight gain.