Hi there and welcome! I'm sorry to hear about your knee pain - have you been to the doctors yet? Did you have an accident (or severe tackle during a game) that may have inujured your knee? How long has the popping and pain gone on? For arthritis, they will do some bloodwork and x-rays on the joints to see if anything shows up. For an injury, they may need to do an MRI to see if you have torn anything in there.
You're too young to have knee problems like this, but it is not unheard of. Depending on what the problem is will depend on the treatment. There are some exercises that help strengthen the muscles around the knee that are supposed help certain knee problems.
I hope you get the help you need - but, football is a rough sport, especially on the knees (I'm sure you don't want to hear that).....don't put off getting this checked out and figured out- risking this getting worse.