my nephew was 7 punds at birth, seemed healthy. low weight gain. weighed 10 pounds at 4 mo checkup. Peds md said feed him more. he is gaining weight and trying to sit up at 6 months but has now aquried a cough,1-2 times an hour, productive with bulging eyeballs and finally catches his breath after everyone is terrified he is not going to. peds md says virus ,wait 3 weeks. now ,the dame after 3 weeks. now peds md says doesn't know won't test for cystic fibrosis. would this be warrented with only mild failure to thrive and chronic cough with mucus production?