or when jogging running.
Patellar tendinitis caused by improper patellar tracking, most likely. Happens a lot.
Take some anti-inflammatories (I like Aleve) and rest a bit. Maybe do some squats.
When the pain goes away, make sure to do some squats (or at least leg extensions, but those have fewer benefits).
And IME rest means lay off the running for a while shoe dude... even a couple of weeks or more if that's what it takes to stop hurting. You'll lose some conditioning, but it beats the hell out aggravating it into a more serious injury.