Looking For Explanation For New Onset Knee Pain. I Have

Looking for explanation for new onset knee pain. I have full ROM, no pain with standing/walking/stairs, no swelling, no fever. Consulted an ortho doc on Wednesday who diagnosed me with a "strain" and gave me a cortisone injection, x-rays negative for fracutre. Despite frequent icing and use of Voltaren lotion I have significant lateral knee pain which radiates into the top of my calf and front of my thigh, especially severe at night. Started following a day of working in the yard with too much kneeling.