The Back Of My Left Knee Is Hurting Wear The

The back of my left knee is hurting wear the calve connects to the hamstring. After I squatted, I felt this pain. I didn't even go heavy as I usually go. I usually squat with 275lbs or 315lbs and that day I did 225lbs. The back of my knee and around my knee hurts when I extend my legs/flex my quads. Any idea what this could be and what caused it? Also what should I do to make it go away. It has been a problem for the past 3 days now. I have iced it and avoided lower body exercises. Thanks.