If your Opthalmologist can't help you, then you should see your regular physician or ER. Mine was from a Strabismus reoccurrence (eye turn) that was born with and was surgically corrected decades ago. I ended up having surgery again on my eye muscles by Pediatric Opthalmologist (even though now Adult). There are many other causes.
https://my.clevelandclinic.org/health/diseases/22203-diplopia-double-vision