Above all, try something. I was thinking about my encounter the other day, with a woman who had not exercised in a number of years, because of pain. If you do NOT exercise, the pain can actually get worse, ironically.
If you have a broken leg, obviously, you should not use it, but if you have limited mobility, such as a bad knee or hip or shoulder, there are all kinds of things you can do to keep your blood pumping, to keep the rest of your body fit, and you should never just quit.
I went to physical therapy today, and at the end had tears in my eyes. It hurt. I did everything, and knew I was coming home to ice immmediately. Sometimes you need to work through pain, to get to the other side, and that is where i am at right now. It hurts every single day, but I get up every single day, do exercises, stretching, yoga, and all the exercises given to me by physical therapy.
I am WAY ahead of where I should be, and can now bend my knee to 100 degrees. It took me three months to do that last time I had knee surgery. I will keep moving because it is the right thing to do.
Just try something. Find something you like, and do it.
Give up one thing this week that you know you shouldn't be eating. Get it out of your house forever. It feels so much better to be fit than one candy bar will ever, ever taste. I do not have one thing in my house that I could eat that isn't good for me. I will not be goaded into temptation, I will not bring one single thing home that isn't something I should be eating. Saying no once in the store is so much better than having to say no over and over at home.
Just do it. Try something, Do something. You will feel so much better for it.