How To Get Rid Of Severe Pain Down The Cartilage In The Right Knee?

WHen I was younger about 15 I was diagnosed with a disease although i forget what it was called, it was explained to me that my muscles that support my nee would deflate and from being in marching band for two years (and the 2 yrs prior the stabbing pain i would get in physical education) wore down my cartilage in my right knee. Supposably i have minimal cartilage only in my right knee. It finally gave out completely and I was on crutches for 3 months. I was reffered to physical therapy and built up the muscles over time. I know I dont exercise nearly enough, but now when I get the dull pain in my knee I am getting a cold feeling like if I was to apply icy hot to it. I get pain all the time with weather changes and over exercising. I am used to the pain and have all types of supportive knee braces, this cold feeling is new. Is it serious?