I don't have CF. But, I just had major abdominal surgery 2 weeks ago, and I'm breastfeeding to boot.
You've got to walk, even if it hurts you have to make yourself walk. The more you walk, the more you'll work the stuff out of your lungs. Its not a CF issue but a surgery issue. I used an ace bandage around my abdomen for the first 2 weeks after surgery. I just took it off 2 days ago.
Also, everytime I started struggling to breath, I would get up and do the cough and deep breathing exercises until I could breath again. It hurt like a you-know-what and sometimes took a good 15-20 minutes before I finally felt able to breath again. But, it works.
As for the breastfeeding, I would strongly recommend you either breastfeed or pump, with breastfeeding being far better. You'll get mastitis if you don't empty the milk, which will make everything worse and you more miserable than you already are.