I'm 22 but have severe pain in only my left knee, standing, sitting, or bending. Knee clicks when I rotate it, no swelling. Any physical therapy ideas?

Knee pain. The fact that you have no swelling is an excellent sign that therapy should improve your clinical course. That said, I would have an MRI to ensure that you have no articular cartilage disorder (e.g. Ocd lesion) and/or meniscal tear. You are most probably experiencing a patellofemoral disorder and possibly a medial plica band syndrome.
Get evaluation. Your symptoms have the findings associated with a possible meniscus tear. Especially the pain and clicking with bending and twisting. Get an orthopaedic exam and you will probably have an MRI ordered to look for a meniscus tear.
Knee pain. Some interesting finding: severe pain, & clicking sounds. Need a good knee exam. Pt, anti-inflammatory med should be done. If no improvement in 2-3 weeks, may consider ortho evaluation.
Need MRI? Sounds like you may have cartilage damage. Physical therapy may not be overly effective. Diagnosis is usually confirmed by mri.