Women have looser ligaments and tendons than men. It's helpful when things need to shift and adjust for pregnancy... Not so much the rest of he time. Combine that with a greater Q angle than men and it means women are more prone to knee issues.
At your age, one of the more common issues is pain from the patella. The patella doesn't track correctly and the result is pain. To know what's going on, you should see an orthopaedic specialist. It's really the only way to accurately diagnose your situation.
You can do exercises to strengthen the muscles around your knee. They are the support structure and can help take some pressure off the joint. Also for every pound you lose, it takes 4lbs of pressure off your knees.
You didn't really say what kind of discomfort you are having and where it's coming from/ when it occurs?
Glucosamine, chondroitin, etc may work. I say MAY because scientific studies show mixed results. Some people respond to it , others don't. It depends on the cause of the pain, how advanced the condition is, and your body's ability to respond to the supplement. Basically if you don't have a noticeable result after 2-3 months, just stop taking it. You are wasting money.