Five year ago I had total knee replacement on one knee because of cartilage loss. That knee is now my "good" and gives me no trouble when hiking, skiing, and cycling. Recently the other knee began to ache. X-rays and doctor's exam revealed minimum cartilage loss but some arthritis. No surgery is imminent, but the pain persists. Cortisone injections and ibuprofen work well. There is nothing else unless I have the knee replaced. All this is a result of age. I'm 74. Fortunately, the pain occurs at night while in bed and around the house when I am just sitting around. On the bike, the skis, or on the trail, little or no pain or discomfort. It's just the way the arthritis is affecting my knee. You would be wise to see a doctor.