Auriel, many of us have faced the disbelief, and it can range from something you just blow off to something really hurtful if it comes from a person you thought you could trust.
I have gotten to the point that anyone who accuses me of exaggeration or making something up is immediately booted from my life unless they can promise never to do that again. It's just too much of a stressor and a drag on emotions and energy, and makes your life worse, so any time you can just remove someone like that from your life, it's wise to do so.
If you can't remove them, then don't engage with them on this topic at all. Don't bother trying to explain yourself to someone who has no compassion and won't listen or believe you. Save your energy for you. I mean this very seriously.
Here, we understand. No one here will accuse you of just not wanting to do things or of making anything up, because we have been through this ourselves. the most important thing is to take good care of yourself and to start doing things that will help you to manage this. And stick around, because we want to help. You can ask anything you want and say pretty much whatever you need to, just bear in mind as Jemima said that this is a world-wide public forum, so you probably don't want to say anything that will identify you, and personal information is usually best left unsaid.
I hope being here will be helpful to you.