I agree with Erica. Especially on the Aspeteme (Spelling). You can find that in the Crystal Light powder, even in the off-brand stuff. I get the worst headaches on those. But, one of the things that I do when I have a migraine coming on. Get ready to go to bed basically. I will sometimes take Ibrophen (Tylenol in your case), and take frozen peas or something FROZEN out of the freezer. I have cranberries that we never use. Depending on the pain level I'll either wrap the frozen cranberries, you know so there is a buffer between the cold and the skin, or just have it go straight onto my forehead or where the pain is most. And just try to relax, breathe, let your mind wonder, and then fall asleep. Don't worry where the peas may fall. I try to sleep it off and usually that works, but sometimes you have to go to the next step. The reason why you have a headache is because...from my understanding....your brain is swollen and it is basically pressing against your skull, hence the headache and pain. So, with the cold compress you are reducing the swelling.
Another cause I just thought of was maybe there is a nerve being pinched. Or your spine is not aligned. Could be a lot of things causing the headache. Stress. I get a lot of headaches. When I was pregnant, my son was on a nerve and my hands were numb. Fun huh? Anyway, you can go to a chiropractor or a massage therapist too. Just let them know that you are pregnant. They can still fix you even though you are pregnant. With that said....I hope this helps. Headaches are not fun. If that stuff doesn't help - talk to your OBGYN and see what else you can take. Take care.