For both of my pregnancies, I got headaches. There didn't seem to be any specific triggers for me, they just popped up randomly, and with a vengeance. I asked my OB/GYN what I could take, and they ok'ed Tylenol for me. Frankly, I don't know what I would have done without it. These headaches were AWFUL and it was like I could barely concentrate until the pain subsided.
But, FYI, I came across this article today about a possible link between taking acetaminophen during pregnancy and a increased risk of ADHD. Check it out for yourself so you and your doctor can make the best decision for you.