Why does my eye prescription keep changing?

Sounds pretty strange. Definitely an ophthalmologist is the doctor you should see. I can't see why your vision would go back and forth. Have you had any hormonal issues going on in the past? Pregnancy can influence vision and that is a hormonal issue. You could have had some totally different hormonal issue that influenced your vision perhaps. Another thing that can affect your vision in what would seem to be unusual ways is cataracts. Then, there are so many other things that can go wrong with your eyes.