Unfortunately yes milly - post-menopause is for ever.
Oestrogen levels decline from the date of the last period for approximately the next two years and they stay at this level. However some effects continue to worsen or develop eg bone loss, vaginal atrophy etc. I wouldn't have thought that night sweats should actually get worse after 5 years - but maybe other things have changed meaning you find them more problematic eg your weight, diet etc? Also thyroid issues can become a problem for older women so could be related to this.
I agree with Dancginggirl that a visit to your GP would be a good idea and especially about the migraines if you haven't had them. You could mention the night sweats and perhaps ask about thyroid too - and the doc may order blood tests.
Have you thought of HRT? That would bring you relief from the night sweats and depending on the cause of your migraines - maybe these too, although tablet HRT can aggravate them.
Hurdity x