Does my dog have cushings/addisons or something else

[MK_212121]

About 4 months ago she started drinking excessive amounts of water and eating more and asking for more food constantly. It has hit the stage that we are having to get up in the night and let her outside to pee.
We took her to the vets a couple of weeks ago and they carried out a blood test that came back normal, a urine test which came back with very diluted urine. So the vet recommended a stimulation test, the first test came back with results which did not look like cushings, the results were showing the results of a dog with addisons, although she is not displaying any symptoms for addisons. Other than the drinking and eating, she is not displaying any other cushings symptoms either, she has a full coat and it is in lovely condition.
The only other thing which worries us is that she has not come into season for 2.5 years now, we think that there may be something going on in the hormone department, which may be causing some of these issues.
The vet has said that we should not get her neutered if there is a chance of addisons as this would affect her stress hormone and can make her poorly.
We have been advised to have a CT scan at a specialist vet, which is very expensive, however we are not sure what else we can do.
Apologies for the long post, but has anyone else ever experienced any issues diagnosing cushings/addisons or anything to do with a dogs seasons which may trigger the excessive drinking/eating please. Any information would be gratefully received.
Many Thanks

[ginger899]

There is never a need to apologise for a long post. It does help to have more detail.

I am afraid I have no personal experience with either Cushing's or Addison's disease.
But has your vet run a Cortisol Creatinine Ratio Test? I believe this is taken from a urine sample. Please do ask if you are unsure if that test has been done.