Aside from the other suggestions, I'm wondering if possibly a knee support while walking would help. I remember those days when I was a teen - the crunching, the pain, the swelling....ugh. I did wear a knee support during my exercising (sometime during the day if I was on my feet for long periods) and it did help a little. If you're doing a lot of exercise walking, make sure you stretch your legs well before and after, and possible do the heat/ice thing as well and rest after the exercise.
Good luck and take care, I know this is not fun. I've had arthritis since I was a kid.