V - if the x-rays and ultrasound came back negative, that is a good thing, it means they've ruled out structural damage to a certain extent. But that's all those tests can diagnose. They can't diagnose muscle imbalances causing excessive pressure on one side of the knee cap and excessive pull on the other. This is a very painful condition but it is functional in nature and can't be diagnosed with imaging. Go to the PT and try to find a good sports PT if you can. They should be able to evaluate your function and determine the cause/diagnose where your pain is coming from as well as treat it. The most common thing I see is tight hips leading to excessive forces at the knee that leads to pain. Usually there is some muscle weakness as well. This is what a muscle imbalance entails.
If you want more information or would like to ask some specific questions, please feel free to PM me. I'd be happy to try to help.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS