I think you've hit upon the issue, as the logical part of your mind knows better but...

Some disorders, like PTSD, run in the realm of irrational thoughts and a patten disbelief in truth.

What have you tried to circumvent having to ask? Does the countering like you shared in the post go on in your before you ask? What professional help have you had regarding this? Sorry for all the questions; the answers are more for you than me.

How about having someone you trust to write down the answer for you... write the question on a card that you can carry, and on that card have the person write the answer. Having trust in the person and the answer, and having it in hand, might help lessen the number of times you need to ask?

Is there something particularly comforting in the answer to this certain question? Have you kept track as to how often you ask it (is it really that many times, that often?) Maybe keep track as you try to lower the number, since it bothers you (and others from what you say)...and tell yourself the NEXT time you feel the need to ask, you just WILL NOT, but read the card and hold out. (Every minute/hour you can stretch it out is progress.)

Just ideas... let me know what you think