can't pop back it hurts the knee!

this all started a few months ago slight pain.. When I sit like an indian or anyime I bring my knee up to cross or half/cross it hurt's to go back down. It's like it wants to pop but it wont!When it finally does it's very painful. Then a release sets in and it feels like aahh finally! Does anyone else experiance this?? It hurts to get it back into place .. Like now for example I aM sitting at the computer legs half'crossed when I go to move my knee back down....ouchy!!!!! A leg brace only helps alittle .. i think it's time for professional help. Do you have any ideas????? thanks much C.G