Horrible headache at 38 weeks!

I woke up this morning with a terrible headache, so I tried drinking some water thinking it may be due to just being slightly dehydrated. I still have the headache, but it's not as pounding as it was earlier. I can't take Tylenol because I have liver issues, is there anything else that's safe to take otc for a headache? I had pre-e with my son, so if it doesn't go away soon, I have to go to L&D and I don't want to jump the gun if it's nothing.