Right knee pain only on left side no swelling can't keep bent 4 long painful when leg is straite it looks like my knee is shifted to left a lot?

Get it evaluated: You need evaluation by an orthopedist and an MRI probably needs to be done. It may very well be a tear although other issues may cause a similar pain.

Many possibilities: The knee is an important weight bearing joint with a complex inner and outer structure. Your pain could be as a result of many different things. A thorough history and physical exam and possibly some laboratory and radiology exams are needed to determine the exact cause. Causes of pain may include: trauma (fracture, tendon or ligamentous tear, arthritis), infection, and metabolic conditions.