I have been experiencing a sharp pain in the lower back and left knee behind me . The knee always hurts me even if bent or stretched. Recently I have been also experiencing a sharp pain in his leg and left arm with numbness in both.

I feel it is so uncomfortable. His back pain, leg , and numbness in her legs could be due to sciatica , usually caused by compression or irritation of one or more nerve roots in the lumbar spine . In most cases , sciatica is generated from a degenerative lumbar disc disease and / or arthritis of the lower spine ( see link below). Now, the symptoms in your arm could not be explained with sciatica , so there is another responsible for that problem. It is possible that both the symptoms of his arm as his leg may be due to a single process , such as multiple sclerosis , which definitely justifies the need for a medical evaluation. If you have not seen your doctor since you asked this question I suggest you to do it ASAP.