difficult diagnosing over internet. could be 2 things here, as well as others! but 1 option is patellofemoral pain - shoud find some exercises on internet for this one, basically invloving stretching some muscles and strengthening others - these need to be painfree. if pain then option 2 is Meniscal injury (tear) unfortunately these do not get better without surgery so you would need to get MRI etc to confirm this and then surgery to fix it.