You have to ice the in knee. Give it adequate rest. Don't walk or run for a few days. Keep the leg elevated on a stool while sitting and on two pillows while lying down. Visit a local doctor who will prescribe pain meds. I cannot prescribe meds as Practo prohibits me from doing so. If pain persists beyond 3 days you need to have it examined by an ortho surgeon. He may order an xray or MRI to arrive at a diagnosis. Good luck!