Can babies get strep? what should i do if the pediatrician won't test for strep because he believes babies can't get strep?

It can happen: But Group A streptococcal(GAS) infections are uncommon in children younger than two to three years of age. When it happens they can manifest with atypical symptoms like prolonged nasal discharge, tender anterior cervical(neck) adenopathy(lymph nodes), fussiness, decreased appetite and/or low-grade fevers. Have you shared your concerns with your child's pediatrician?

Mixed issue: The prime reason for treating strep is the prevention of Rheumatic fever, which is unusual under 5 and never seen in infants who have an immature immune system. Yet 5-30% may be strep carriers depending on the time of year. If all infants are tested for strep at any visit, many will be exposed to unneeded antibiotics. If there is a clinical reason to test, it should be done at any age.