at 20 you are 'growing out' of OS now, if that is what you had, it shouldn't bother you once you stop, whcih may be now. regradless the management for OS is do it if it doesnt hurt, but rest when it does. you will need to do eccentric patella tendon loading to strengthen the area and this is safe as long as pain free. agree with others, release the tight stuff, and ice cube massage or ice the area if it is sore following the exercise. be patient load it up gradually over 6-8 weeks. 3x10, 1 x day; then 3x10, 2 x day; then 3x10, 3 x day, then increase to 3x15, 3x20 etc. then increase speed - you may have to get taught how to do these but may be instructions on the net too.