I had my appendix out about 11 years ago. It's actually sort of odd how they found out it needed to be removed! I was having an ultrasound to check on my gall bladder, and they stumbled across the appendix and said "wow, that needs to come out!" I wasn't having any symptoms or anything. When they told me I needed surgery I just laughed and asked "can I call my mom first?"
After the surgery I was very sore. They had gone in through an existing scar, but even so, the site was painful. One thing I was surprised was sore was my heels! I didn't realize how hard and unyielding that surgical table was. My lungs took awhile to bounce back too, but they eventually did. Give yourself plenty of time, and work up your stamina gradually.
One thing that can help is to stretch your arms up over your head and hold them there until they start to feel heavy. Breathe in as you lift, and out as you lower them. Try doing this several times a day. It's good for relaxing and coping with the pain, as well as helping bring back your lung function.
Hang in there!