Suggest Remedy For A Sore Knee

I had a slightly sore knee at work last night. It would hurt if I stretched too far but was more bothersome than painful. I took it easy all night and went home and just sat around. Out of nowhere it began to hurt intensely and throb mainly on my upper thigh. It's persisted for about 4-5 hours now and even my knee now hurts as well. I thought I pulled a muscle but it has gotten worse without even moving/doing anything physical. What is wrong?