My knees hurt even when I lift something slightly heavy.

When I was in my twenties, I often carried heavy objects and overworked my body, which caused my knees to hurt. Since I stopped that activity, I have been fine, but now my knees are hurting again. When I lift heavy things or walk with a heavy bag, my right knee aches sharply. Then, after a few days without carrying heavy objects, it tends to improve. However, I feel that my knees hurt more when I sit for a long time or don't exercise at all. Conversely, walking and moving my body seem to help the knee pain go away faster. When my knees hurt, is it better to do light exercise rather than rest?