Well I Am A Male That's 15 Years Old And

Well I am a male that's 15 years old and well I've been having knee problems idk what it is but when I'm in weight lifting I go down to parraell and I hear a pop and when I come up it hurts. P.S it is my right knee. Then whenever I'm home I will bend my knee my left knee just goes all the way but my right knees stops when it does go through I hear a loud pop and then when I lift it back up I hear a rubbing sound. All I want to know is what it is and will it last forever