My son was also diagnosed when he was 2 weeks old. When we went for a checkup when he was 4 weeks old I was pretty sure I had strep so they cultured both of us to see what was going on and it turned out that we both had strep, his CF clinic had told me he should be cultured because babies carry strep in their nose and chest. That is when they put him on the upped doses of the xopenx. I would call the CF Dr. and see what they say.
Also I wanted to tell you that after our son was diagnosed my husband had the same reaction after finding out more, that he too may have CF. He had a chest xray and a sweat test that can back fine but we still aren't convinced so we plan on getting the genetic test when our insurance kicks in. Best of luck.