I know this might not help, but I was kinda that way when I was pregnant with Scarlette. I had a LOT of headaches until about the middle of the 2nd trimester. I don't know why. I had a bottle of fast acting tylenol in my purse at all times. I had at least 1 bad one a day. It sucked. I was also extremely thirsty, not drinking as much as you are saying, but a lot. I would go through a gallon of juice and a gallon of water a day. See, I am weird though, water NEVER quenches my thirst. Ever. It just makes my mouth feel dry. So, I would drink one glass of water, then a glass of some flavor of juicey juice ((normally apple or punch)) and that would help keep my thirst at bay a little better. I would also get dehydrated a lot too, I would wake up every morning with cramps ((from not drinking a lot all night)) and my doc told me to put a glass of juice/water on my night stand and put the alarm on my phone on ((vibrate of course)) every 2 hours or so to wake up and drink during the night. By the next month I was waking up on my own to drink, and it got better. With the HB ((I had it in all 3 pregnancies, but the worst was with Scarlette)) I would eat bread and then take a tums, and that helped too. Mention it to your doc, he may be able to give you other tricks.
But, I did hear that headaches during pregnancy means that it's a girl, so good luck
