I'm only 18 years old, but over the past year my knees have started to ache worse and worse and now it's pretty much a constant achy stiff feeling in my knees at all time, it's slightly worse in my right knee than my left, i know this isn't due to an injury, and i'm not very active, but the pain is worse when i'm active (ie: walking a lot, running). could this be arthritis? or does it sound like something else? please help i am completely broke and can't afford to go to a doctor unless it's an emergency.