Welcome to the forums!
Looks like you've had a really tough time with injuries.
You sound like a strong person though, and I'm sure you'll be able to pull through and achieve your goals!
If you have the access to a gym there's lots of low-impact equipment you could exercise on. Eliptical machines are great!
Are you planning on just upping the amount of exercise you're doing, or are you going adjust you diet as well?