Hi rosi, or anyone else who can help, I've 2 points I could use help with please

1) probably 8 months ago I started getting pain in the middle of my chest, I can't place when I hurt it or even what starts it but the pain comes while grappling if someone for example has side control and has their weight on a point ie elbow in the middle of my chest, Or if doing standup and some teeps me hard in the middle of my chest, it doesn't feel like a muscle problem, what could I have done to my chest? And how could I fix it? (please don't say rest)

2) sometimes my knees feel like they've took a bit punishment and don't feel 100%, my dad has bad knees due to arthritis I think it was and had an operation some years ago, is there any prehab or anything I can do that will help delay any problems?

Thanks for any help given