Some migraines are triggered by an electrolyte inbalance.
It is possible (and likely) you are drinking more fluid at the weekends.
Not everyone holds onto the electrolytes they need when they increase their fluid intake suddenly.
In some countries (not the UK) if you went to A&E (ER) with a migraine you would immediately be put on IV electrolyte's.
Try keeping a fluid balance chart every day for a couple of weeks, if thats a bit much (it probably is) then just keep track of your daily fluid intake during the weekdays and seeing if it ups at the weekend.
Theres a trend for people thinking drinking lots of water flushes out toxins which in a way it does but it doesn't work when the fluid intake is upped just on the weekends and it doesn't work for people who don't hold onto electrolytes well, it instead has quite a detrimental effect.
Don't answer this on here, but do you find you pee more at the weekend? If so it's possible thats your body trying to maintain electrolyte balance (concentration) by getting rid of fluids.
An alternative that might be worth trying is adding electrolytes to whatever you're drinking.
This sort of thing thats neutral and can be added in drops to anything works well.
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