You are absolutely NOT being unreasonable.
At this point, you are the patient. Your husband has shared your confidential medical information without your permission.
It feels to you like he's shown people scans of your body because that's exactly what he's done! Yes, the scan pictures include the baby as well, but your partner has shared your medical records. He isn't showing his colleagues the baby's medical records, because the baby isn't legally a person yet. You are not just a mechanical incubator for his offspring, you are a person in your own right.
Of course it's understandable that he wants to share the news about the baby, and get support for his concerns, but he really really doesn't have any rights to share your medical information without your permission. It's absolute bollocks that you 'have to' tell everybody once you've got past the halfway mark- you need to inform your employer at the legally required time, and it's sensible to inform them of health and safety issues, but there is no obligation on you to tell anyone else. You don't even have to tell your husband, or invite him to the scan.
Regardless of the opinions on the thread, your medical records are private. Your partner has no rights until the baby is born.
You're clearly worried about your mental and physical health, but the fact that you consider yourself to have mental health and anxiety issues doesn't mean you're wrong, because you're not. It would be helpful if you and your husband could find a way forward that's acceptable to both of you, but trampling all over your right to medical confidentiality is not the answer.