Body pain while playing. My condition?

I have been gaining a lot of weight after my marriage and decided to Atleast try shedding off extra kilos. So started playing Badminton on weekends with friends. We play for a few hours. Whenever I try to warmup I feel a few problems 1. When I start stretches on my arms(similar to bowling action) in circular motion I hear a knock everytime on one round completion. I fear more warmup may make things worse so I stop the stretch. 2. Once I start playing and hit a few smashes, area near my elbow and forearm starts paining a lot and it becomes very difficult to play going forward until I rest for sometime. 3. I start feeling a lot of pain around my knees. I had ACL surgeries done on my left knee twice and had recovered well at the time but now it has started paining again. More of it on the other knee i.e. Right knee. Any suggestions on what I could do to improve my condition?