T182T writes:

My problem is that my AME has always considered this well-controlled
condition to be not serious enough to bother with the FAA procedures,
and not worth declaring. So all these years I have declared that I am
not taking any medication, when this is not in fact true.

It's your signature, so you are the one making a fraudulent declaration, which
is not good (for you).

My question is, now that I have to change AME, is this the time to
"come clean" with the FAA and declare this condition?

You need to talk to a lawyer, not an AME. This sounds like a very delicate
situation that will backfire seriously on you if you don't handle it with the
utmost care.

I have never lied to the medical examiner, she is the one who suggested
I not declare it, stating that I do not have a serious medical condition
or a higher chance that the average person to have a health-related
incident when flying.

In practical terms, she is right, but legally, she's wrong. You have to
declare it, and so does she. Unfortunately the ultimate responsibility is
yours, because you're supposed to know that you must declare everything, and
it isn't necessary to be a doctor to know this and do this.

The AME might be in the wrong, too (and now everyone to whom she has given a
medical is going to be suspect), but you need to worry about yourself.

If I don’t say this to the new AME then it becomes me who is not telling the
truth, and I know the FAA takes a dim view of this.

You've already failed to declare it, which the FAA views very dimly as well.

Question for those who really know - What’s the best thing for me to do?

Find a lawyer who is an expert in aviation law and follow his advice. Doctors
are not lawyers, so they cannot help you here, as this is a legal issue, not a
medical issue.