I was running yesterday and at the end of my run, I experienced a very strong soreness in my left knee, right below the kneecap. This has been happening randomly during my runs for the past few weeks. I run 3 days a week, and sometimes it bothers me and sometimes it's fine. I have only been running on treadmills for the past couple years. The soreness I experienced yesterday was the most intense it's ever been. It was still sore when I had my workout this evening. I do the Bill Starr 5x5 routine which has a lot of squatting, but I never experience this knee pain when squatting; it only happens when I run. Does anyone know what this could be? Is it tendonitis? I'm not a running n00b; I've been running to varying degrees for years now.