Replying to Knee Problems

Ok, so over the past couple years ive had knees problems, nothing like torn ACL's or anything but ive just had chronic pain and I started to notice it a lot freshman year in soccer. Now in junior year, and every season after I ski which is about 3 times a week I can barely walk after I get home, so I was wondering if you guys could help at all, either to give suggestions on how to strengthen my knees? or to do something so they wont hurt as bad. Sorry if this has been answered before.

-Bill