Can't correct - constantly changing script

During the past year I have been to three doctors and none seem to be
able to get my prescription right. Each seems to claim that my
prescription keeps changing -- Does this sound right? I hae worn
contact lenses and glasses for about 25 years and havenever had a
problem like this. My contact lens prescription for years was -8.5.
One day I seem tohave receieved the right prescription and the next my
visions is blurry and awful. I have had my eyeglass lenses changed
three times, and, even now, they aren't quite right. I can feel a
headache developing and I know (from experience) that I will be taking
Excederin for the rest of the day. I am 43. Recently had a physical
and everything checked out OK. ANy ideas what is going on or what I
should do?

 

Thank you. I would not have thought of asking for a corneal
specialist. BTW -- is a rigid oxygen-permeable lens the same as a hard
lens?