Can muscle unbalances cause pain in si joint area on one side?plus nerve pain down leg. had mri and showed no disk problems, pain in side really sharp

It: Can. This can lead to gait issues which could also lead to the muscle and nerve pain. Physical therapy would help this issue. Talk to your doctor

Yes but may not b: Yes muscle involvement can be involved, but also the facet joints can also cause radiating down the leg. As part of your evaluation the other thing to consider is if the nerve is being irritated outside the spine such as by the piriformis muscle . These are things your physician will need to try to evaluate and help you

Ask M.D..: Ask your doctor if this puzzling pain could be piriformis syndrome where the piriformis muscle in the gluteal area compresses the sciatic nerve and causes both unilateral pain in the buttock and sciatic nerve pain down the leg. There are other causes of sciatica that your doctor could relook at too.