Glad to be of help.
I understand that feeling of the looming yuck. Let's see what I can do to help with that. I have a few suggestions.
One thing you can do that's become fairly common practice in a few fields of medicine (dentistry and gynecology amoung them) is offering anxious patients medications to help calm those feelings, usually a benzodiazepene of some kind. When that's done, that will just be a one-time medication you can take the night before and/or day of an appointment. I'm not an anxious GYN patient, but I am very much so with the dentist, and I find that very helpful.
I'd also suggest that you do what you can to choose a GYN who you just generally like and feel comfortable with. Obviously, if we have mixed or negative feelings about someone -- or they feel like a total stranger -- it's much more likely that the kind of experience you had is going to happen. On the other hand, if we have a more established relationship with someone, if they feel like a real partner in our care of ourselves, and if we can have conversations about our feelings with them ahead of time, it makes a more positive experience a lot more likely. In that search, I'd suggest you ask clinics or receptionists what the particular doctor tends to do to help anxious patients and let them know you are one. I get that might not feel like the best word for how you are feeling, but it's the umbrella term often used in healthcare, so they'll know what you're talking about. If you feel comfortable doing it, you can also say that you have experienced some medical trauma in a previous exam and ask what they do for patients in that spot.
Once you feel like you may have found someone, you can ask for a consultation appointment that does NOT involve any kind of physical exam, it's just you talking with the provider and asking them the questions you want to. Since you just had a bimanual exam, you could even ask for this for someone to talk with about your menstrual stuff. They might want to do some bloodwork at that kind of appointment, but they could refer to the records of your last exams for any information they needed as a result of that.
I also want to point you to this article -- https://www.scarleteen.com/article/bodi ... dern_guide
-- by Caitlyn Tivy, an awesome PT who writes for us. It includes some variations for exams, but also talks some about how a bimanual exam is something a lot of folks don't even need anymore, and may well be something you can usually opt out of entirely.
Lastly, we can talk some more here about all of this to help you process your feelings some more, and that includes your previous sexual experiences you mentioned. By all means, with a history of feeling like that kind of engagement with your body -- sexually, medically -- has not been what you actually wanted or like something you felt able to say no to, it's not at all surprising it really messes with your head. Working through some more of that and maybe talking about how, moving forward in every arena, you can start only having people be engaged with your body on your terms, might help, too.
How does all of that sound?