Peroxideglader, the problem is the NHS is very rigid with a 'one size fits all' policy but they are supposed to be guidelines, not gospel. If you can't take that amount of progesterone, you can't just magically flick a switch and make yourself able to because of the NHS guidelines which, in my opinion, are OTT on progesterone doses anyway for many women. The whole thing needs to be far more flexible.
If you have a problem with progesterone, the only thing you can do is reduce the dose and then have a scan in a few months to see if you are getting adequate thinning and clearance, there is no other option. It's pointless to slavishly take too much of it, suffer when you don't need to and then end up ditching it altogether when there are other options. If I took the NHS stated dose of progesterone, I would get overthinning of the womb which would cause all sort of problems - I would have a permanent migraine too.
Obviously everyone is different and there is no guarantee you will need as little progesterone as me, you might need more, but the best thing to do is to find out how much you need and stick to it.
I hope that helps.