Terrible migraine 14 weeks 2 days

Throughout my life I have been having migraine. For the last 2 years it was more like alarming the arrival of my periods the following week...it used to be terrible but lasts for 3 days maximum

I am 14 weeks now and I have frequent terrible migraines from 12 weeks..my gynecologist doesnt seem to be worried about it but I have had enough bearing it. it's so bad I can hardly move! I am not dehydrated as I drink atleast 2litres a day. I have seen many suffering like this during this time but i am so curious to know what can diminish it and what causes it in the first place!!