Suggest Medication For Pain In The Knee

I am 27 and for years I have had knee pains like I could not bend down but if I took glucosamine it would go away. Now in the past month it doesn't hurt when I bend down but when I extend my leg my knee cracks. Its not extremely painful but there is a consistent pain. The glucosamine is not working and I have never had any sprains or broken bones in the past. What is happening in there?