Knee Pain

I am 34 and have always had great legs/knees for running and other forms of cardio. Just before Easter I went onto an elliptical machine for an hour. When I got off my knee felt a little strange. Over the next week it worsened. Now it is 1.5 months later and sometimes it hurts climbing stairs or standing for long periods of time. It is a nagging and burning pain (right knee a little towards the outside.. it doesn’t radiate to my thigh or anything). Its not debilitating, but it is very annoying. Basically I want to rule out what it isnt – my question is.. if I had an ACL/torn ligament, etc.. would it be a lot more painful than it is? Usually rest and ice with ibuprofen helps, but it always comes back if I am on my feet for any length of time.
thanks,
scott