Knee injury

I recently injured my right knee while running. The pain is on the outside by the joint and comes on almost immediately when running or when i walk up and down stairs (also at random times eg. sitting at a computer) and usually goes away when i stop the activity. It happened over a month ago, since then i have kept it elevated, bandaged, iced it, used magnetic therapy, tried stretches, taken cod liver oil and glucosamine sulphate but as yet have seen no improvemnt at all. I’m pretty sure its not my IT band as i believe it would have healed by now. Has anyone got any idea what it could be? I have recently also appled for the Royal Marines and the injury has caused me to cease my training. Any Help would be great.