I hope your head is better today daisie? When I get that hangover (but not a hangover!) migraine headache with exhaustion it lasts for 3 days, then my head clears and the fog lifts....
As I said in my post below it should settle quickly if it's oestrogen induced but maybe will take longer if it's the progestogen, and if it doesn't at all then a different preparation may be needed.
Hurdity x