My knee pops and hurts really bad when I sit and stand, what could be the cause of thiis?

Possible plica . Usually plica syndrome is characterized by pain near the anteromedial (in front and toward the midline) side of patella (kneecap). Usually the pain is associated with bending of the knee and is irritated after and during exercise. Usually, no other symptoms other than pain is present, but it can occasionally be accompanied by swelling of the knee after prolonged physical activity.