This can be one of several things including a physical injury to the area, gout, arthritis, etc. With these vague symptoms and the absence of an x-ray/mri or physical exam it is very difficult to pinpoint the exact cause.
The first step is to get in with your doctor that can doa physical exam.
He will then most likely order an x-ray or mri to determine the cause.
That's what I thought. I was just trying to prepare myself a little.
Over the counter pain medications like ibuprofen and normally used in cases like this. You may also find relief from elevating the area and applying cool compresses to the knee.
Thanks, XXXXX XXXXX to try the cool compresses.