I Have Intense Pain In My Left Knee. Cannot Stand

I have intense pain in my left knee. Cannot stand on it, very difficult to get up out of chair, cannot bend it much and cannot straihtened out.X-ray showed a little arthritis. Orthopedic Dr examined it, said the knee cap is inflamed, swollen, gave me cortisone shot under knee cap and ordered a MRI. I had cortisone shots in my other knee 8 years ago and the knee pain reduced a lot and the knee felt better. Its been 8 hours since i got the cortisone and no relief. Any idea whats wrong with knee and what are options to help it