I am the mother of a cf child, and do not have cf myself, but I just wanted to say that I weighed about 110 lbs at your age. It sounds like you are doing quite well considering what you are up against. I think sometimes we may stress about the weight thing too much, thanks to the medical profession. Try not to think in terms of numbers on a scale, but rather how you feel healthwise. If this is a concern then I would imagine that you are doing well otherwise, which is a good sign.This is simply my opinion and I do not mean to undermine how you feel, because I will never walk in your shoes, but I wanted you to know that I weighed less than that as a 'healthy' adult.