What Causes Reduced Joint Pain While Exercising Which Is In Excess While Alseep?

Hi I had a flap tear medial meniscus repair 3 months ago,30% of the menscisus was removed. I have carried out regular physio but still have moderate pain in the same area, I have grade 1 and 2 arthritis in the joint but wonder what may cause the pain.Its better after exercise but noticeable when Im asleep