Why do my teeth still wiggle 8 months after braces removal?

It is unusual for your teeth to be wiggly after eight months.  The primary one that comes to mind is that you have a traumatic bite.  IOW, your front teeth hit heavier than your back teeth.  That can happen if they were trying to close spaces when there wasn't "room" for it.  There are two sure signs if this is the problem.  First if you close lightly together into a normal bite on you back teeth, then place a finger on the front of your upper front teeth. Then squeeze all the way together.  If your front teeth move forward (even a little) as you squeeze, you have a problem.  Second if you tend to develop some upper spacing when you are not wearing your retainer.  If this is the problem, I would certainly notify your doctor.  It will not get better by itself.  There are some pretty easy fixes for this.