I'm so sorry you're having such a rough time.
It's good that you have a specialist consultation in a couple of days. Clearly your current treatment is not working.
My advice would be not to rush to take any more antidepressants, particularly given mirtazapine hasn't been helpful. They are seldom effective for psychological changes associated with menopause, and not first line for this indication.
If you can get it, a short supply of as required diazepam is both safer and more effective for acute anxiety, and this avoids becoming parked on daily psychoactive medication that can be difficult to come off.
I would taper down the mirtazapine very slowly, particularly if you have been on it a while.
Having a few sessions with a psychologist if you can afford it or access it through your employer or the NHS can also be a much better option than antidepressants as this can help you develop longer term skills to deal with anxiety and panic.
Also don't forget about testosterone when you have your specialist appointment. This can be a major player in psychological wellbeing, alongside estrogen.