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Without the possibility to obtain a detailed history and a physical exam, I cannot tell you what the cause of your symptoms is.
Pain in both legs could be from multiple causes, and these should be investigated. History and physical exam gives a clue in most cases, and studies can be ordered accordingly depending on the possible diagnosis.
A common cause of pain in the legs, specially with exertion (walking) is problems with circulation. Vascular problem leads to decrease flow to the legs, causing pain. However symptoms commonly resolve with rest. A good exam checking pulses can make the diagnosis, if there is doubt, special tests can be performed.
Neuropathy causes pain, numbness, tingling and other sensory symptoms, and frequently affects symmetrically on both sides, in a “stocking” pattern. Sometimes depending on what nerve is affected and its distribution, patients have unilateral symptoms. The pain could be burning, throbbing or like “electric shocks”. Can fluctuate throughout the day and get worse at night. There are different types of neuropathy, and different causes, being diabetes one of the most common. Neuropathy can be diagnosed with history and physical exam. If there is doubt, and to better classify it, EMG-NCV helps. Sometimes, when these are normal, other tests are needed, including skin biopsy. To look for the underlying cause, blood tests can be performed to rule out the most common causes, however many times the cause is not found.
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Joint problems can produce lower extremity pain, and again, history and physical exam will help with determining this.
Regarding back problems, the fact that you had surgery at one spine level does not prevent you from having problems at another disc level. The symptoms could be similar to what you had experienced before, but in a different distribution. Some patients can have symptoms from the same level they had surgery before. I cannot really say with if the symptoms you have at this moment are or not related to your previous surgery. And some patients present with low back problems but their main symptoms are in the legs, and no specifically in their "buttocks".
As I said, for the diagnosis of pain in the lower extremities, most of the information to guide the work up and eventual diagnosis, comes from a good history and a physical examination. Without being able to obtain them myself I cannot tell you what the cause of your symptoms is.
I think you should discuss your symptoms with your physician, and find out what he/she thinks you have at this moment. If symptoms persist, or no cause is found, considering an evaluation by a neurologist may help.
I hope this information is useful. Good luck.