Both of my eyes are off-center but only one at a time and I can switch at will.?

Intermittent tropia. Can be exo (out) or eso (in). Depending on which eye is fixating is the reason why the strabismus is alternating (switching which eye is straight).
Possible crossed eye. You may have so called crossed eyes, or strabismus. I would obtain a consult from either optometrist or ophthalmologist to evaluate the condition and be treated accordingly.
Intermittent tropia. As an adult only hope for fixing is surgery.