Weight loss?

I am 16 and 210 pounds. I don't look like I am that over weight but I am. I had this knee injury that makes it really hard to exercise. Had to have 3 surgeries and is taking physical therapy right now. But it is just helping my knee not my body I used to play sports to maintain my weight but I can't do that anymore. I can't afford to go to a gym. So what can I do to lose weight?