My suggestion would be to walk, even though it's difficult. Set yourself a goal and walk every single day. When it's easier to walk a short distance, add just a little bit of distance to that. Continue and repeat. Work up to a good distance, make it a habit. Then set your next goal.
But my suggestion is not as good as whatever your doctor can recommend. He knows your health, you're not his only patient who has this combination of conditions, and he can even refer you to a physical therapist to get you started. I would make an appointment to talk to him about what you can do.