Knee pain for about a year, medications as physical therapy don't help, & nothing shows on x-rays, mri, & bloodwork. what could it be?

Difficult question: Without examining you or knowing where your pain is it is difficult to answer that question. If it is behind the knee cap it could be patella femoral syndrome. This is a patella tracking problem that often has normal tests although it should improve with pt and /or bracing. Another option is that the pain is referred from another source such as your hip or lower back.

Difficult to say: Without a physical exam. However, it sounds like a muscular issue, like specific quad weakness that is not being treated correctly by your pt regimen. Do you have tight hamstrings? That can cause knee pain. Any evidence of patella not tracking correctly? Patella - femoral syndrome is often missed as there are no specific x ray findings. I am assuming they have ruled out osgood schlatter?