Knee pain: Is it patellofemoral pain syndrome?

Patient: I’m 20 yrs old, I’ve been having knee pain when I sit. The pain is for a second or so.. What is the problem I have? I consulted a doctor, he said that it was patellofemoral pain syndrome.. What is this condition? I don’t have any x rays or MRI. I’m experiencing the pain since 2 weeks.

Symptoms: Knee pain and muscle pain near knee