Ive Had A Pain In My Left Knee For About

ive had a pain in my left knee for about 2 months now. The only time it hurts is when i squat, walk down stairs, and go frm sitting to standing. Sometimes it hurts right when i wake up and try and lift my leg when it is straight as well. All other times it is fine I can run, walk, jump, wear heels etc with no pain at all. Any information or helpful suggestions to make it feel better would be appreciated