what coul be the cause?

[munik]

My doctor sent me to do an x-ray, and it showed absolutely nothing, no problems with or any changes in spacing between spine segments, spine curvature or anything else, so to make it short - nothing to concern.

Doc gave me ibuprofen for pain and sent me home telling me that pain will go away.
The pain started when I a awkward move with my leg (and I didn't warm up at all). After that the pain (in my buttocks, one than another - including pain when I sneeze, cough) it goes through some cycles - first I feel pain in one of my buttocks, than it settles slowly, after that pain goes in other buttock than it also settles down. No pain when I'm in still position, pain mostly occurs when I suddenly do some move, but sometimes it hurts when I simply walk (the pain is usually located in the lower part of my buttock. When it hurts just by walking I absolutely can't run ( actually I can but when I do, I have sensation of like"lightning" going through my buttock, rarely down my leg.
So the pain comes and goes.

This has been happening to me for last year (after x-ray). I'm little confused. So my question is "is it possible that all this pain is caused, and still not to be sciatica or other problem caused by spine"?

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One more thing, I  never have pain in my lower back, I can do all the test like bending over, standing and walking on heels or so without increase of pain.

[kittyluv1]

If the x-ray showed no evidence of structural problems in the spine -- especially no significant sign of degenerative disc disease or arthritic changes,  your symptoms could be related to a muscular injury such as piriformis syndrome,  It is the inflammation of the muscle that might be causing irritation of the sciatic nerve and therefore is not related to any disc problem in the lumbar spine,
The symptoms are very similar to the radiculopathy associated with sciatica, but the origin of the pain is different and needs more definitive treatment.  It would be beneficial to have an evaluation from a registered physical therapist and determine if this might be your pain generator.  Treatment would involve stretching exercises, ice/heat and medication to reduce inflammation.  Deep massage and myofascial treatment can be helpful in increasing the blood supply to the muscle and decreasing any associated spasm.
If piriformis syndrome is suspected and the above treatment options don't provide sufficient relief, an injection (corticosteroid and anesthetic) administered into the muscle itself may help decrease spasm and provide more effective pain relief.
Discuss these options with your doctor.  Even if piriformis syndrome is not the definitive cause, you could benefit from a short course of physical therapy to alleviate your current symptoms and learn how to reduce your risk for any further injury.
Best wishes ----