I know
. Flashbacks are yucky and, as you say, can just turn up in an instant - they can truly take the wind out of your sails
I used to beat myself up a lot over it - chastising myself for not being over it and cursing others for not waving a magic wand to get be through it.
You were hurt, and that takes time to heal. If it is possible to ground yourself when or after you're having a flashback then I advise you do - continually remind yourself that you are safe now - that it is NOT happening now, that it is in the past and you can work through this. When you are able, making a couple of notes about what brought it on and how it felt might help - you can then either take it to your therapist or process it when you feel a bit more stable.
You may like to have a read of this:
http://kalimunro.com/wp/articles-info/t ... any-better
I know it's tough - it's annoying, upsetting and downright frustrating - but keep working through each bit and you'll get there
. You've come this far and I reckon you deserve a good-old pat on the back for getting to where you are now.
Be gentle with yourself.