I used to have a constant low-grade headache. It took years of allergy shots, some other medications, and even some acupuncture for them to become a periodic occurrence. Granted I haven't had an allergy shot in a month and a half at this point (which probably doesn't help) but they also say headaches are a common occurrence during pregnancy due to increased blood volume and whatnot. Then there is the possibility that my eyes/vision could be shifting too. I'm not sure if my eyes are hurting because they're straining more and causing the headache or if they're hurting because of the headache.
I really should not be complaining about this suffering as I know I'm getting off very easy compared to many during their pregnancies. (I haven't vomited once and only have a bit of round ligament pain, an itchy back, and some discomfort finding a good sleeping position.) But man, I could do without the headaches. You don't realize how much you were hurting until they go away - I swear it amplifies the pain when you do have a headache.
I caved the night before last and took some acetaminophen to knock it out. But less than 36 hours later and it's back.