What Causes Knee And Joint Pain?

hi i.m 28 years old ,weight 54kg my problem is i think my joints of knee bone are reduced day by day bcoz a liquid type material release from pennis when i met my friend or hug him i have no sexaual relation with him but my health knee joints seem to be hollow inside there is no skin or charbi on it i f i touch knee cap i feel pain so pls prescribe me mediceines to cure this diseases