Swollen knee for a week. Can't squat or bend my knee won't support it. Pain. No injury I didn't fall noticed the pain getting off couch week ago?

Hard to say. There are a number of possibilities and usually a detailed exam with appropriate studies can make the diagnosis. Probably the three most common causes of painful swelling in the knee of a 20 year old without i injury would be: an overuse tendinitis around the answering bursa, an inflammatory condition, or an a traumatic internal derangement of the knee. Consider being checked. Thank you.