I have had this pain for years in my right knee cap. When i extend my leg str8 out i have this terrible pain in my knee cap and it also does it after i jump. Also it feels like there is some liquid on my knee cap. I have no idea what it may be but I dont think it is supposed to be like that.

Does anyone know what may cause this or what it is that is wrong with my knee? Also what is any remedies orwhat i need to do about this?

Any help on this subject would be appreciated!
Thanks everybody for your help.