Horrible Headaches

I'm 16+4 and I have had horrible headaches since I was 12 weeks. I drink 4-5 water bottles a day (16oz) so I'm not dehydrated? I don't take Tylenol or anything I don't want to medicate unless I absolutely have to. So far no one I've talked to gets these horrible debilitating headaches and my doctor tells me drink more water but lord I already drink so much. What can I do for them and am I alone on this on.