I understand how you are feeling. My older daughter, Kayla, was dx with CF at 14 months old. I was already five months pregnant with my second daughter, Hannah, at the time. We didn't do any prenantal testing on Hannah. She was tested at birth via blood samples (although the test came back only a carrier because one of the mutations was not tested for) and then again at one month of age, via sweat test and genetic testing for the same mutations that her sister has, both coming back positive.
Although I didn't have the 'official' word on Hannah the first month, I knew in my heart that she had CF too. Even after the first test came back that she was only a carrier, I KNEW it was wrong, although everyone around me was rejoicing. She wasn't having symptoms, I just FELT like it was wrong. Our CF clinic still did their own testing even though the pediatrican did it at birth, and I am thrilled that they didn't even think twice about testing her themselves.
My sister has three sons, and only her oldest son has CF. We do not know carrier status of the other two.