Will my knees survive?

0ver this summer ive gone lazy due to high work load and vast quantities of food. my upper body hasent gone through much weakness. i still have energy when needed..but my knees..oh lordy. more specifically my left knee. behind the kneecap it hurts to extend i push my kneecap down alittle i hear the popping and pain. my other knees fine. i wanna do some serious running and squats so i dont c completely let go.. but would that help cure the pain and weakness of my knee. it feels like its ready to just snap if i didnt have two legs.. can intense excercise cure it? i know obviously if i lost a few pounds its less stress on my knees..but it will still be weak wouldint it. what are my options