Suggest Treatment For Swelling And Pain In The Knees

My right leg has been swollen and achy particularly at the knee, I had no injury that I know of, had a message a couple of days before it started hurting and I was told that leg was very tight from the upper thigh to the ankle. It started hurting a couple of days later, late at night. It does better when I lie down, sitting for too long it gets stiff and sore, and if I m up walking or active it gets really sore and then at night I find it throbs. Ive taken ibupropen and i have iced it, makes it feel better for a short time. What do you think is wrong, its not red or warm.