Is it possible my spine could be unstable? i have had 3 spinal fusions and my latest was done 7 months ago.. now my back is so sore and feels very unstable when i move etc...

Depends: where did you have the three prior surgeries and by whom? maybe it is time to think of second opinion.

Yes: Yes, it is possible that someone's spine is unstable, and this is one of the reasons a fusion is done to begin with. In your case with three prior spine surgeries, you would want to discuss directly with your surgeon the specific cause of your current complaint.

Spinal Fusion: Samuel573, Difficult to say, but revision operations usually are more painful and take longer to recover from by a patient's perspective. If a fusion operation was performed it should actually make your spinal column more stable as the goal was to "fuse segments of your spine together so that they do not move independently anymore. Oftentimes instrumentation is used to assist with fusion.