How to fix it: See a doctor.
You simply cannot rely on information given online, even if it seems well-meaning or someone's had a similar pain. You just don't know what's causing it. Get it diagnosed properly.
When I had Runner's Knee I did a little self-diagnosis by Google before seeing a professional, and had read an article in Runners' World comparing RK to a similar problem called ITBS.
By Google and RW I had ITBS. Absolutely without a doubt. The symptoms were opposite, and mine matched ITBS.
Both the physio and podiatrist whom I saw diagnosed Runners' Knee. The treatments are different. I'm well and running again now, after having correctly treated my Runner's Knee. I don't know what would have happened to it if I'd treated for ITBS.
Always see a professional, especially when it's as bad as you're describing.
Deb, in New Zealand