My Knee Has Been Having This Issue It All Started

My knee has been having this issue it all started on deployment i cant stand too long without a stinging pain in my right knee and also when i walk itll sometimes pop out and also if i run itll sometimes pop out and if it doesnt my whole knee will be extremly tight causing more discomfort the military doctors didnt do much for me besides shove there finger under my knee cap and say everything was tangled and there is nothing i can do about it which i feel isnt right if someone could help me i would be very grateful