Have you started or changed any supplements or medicines recently?
I started taking liquid cal-mag toward the end this pregnancy, figured it couldn't hurt getting some extra Calcium since I can't eat dairy and dark greens weren't appealing to me. But shortly after I started taking it I got a higher than normal BP reading at a mw apt. followed by a killer headache that wouldn't go away later that day/next day. DH took my BP again and it was pretty high (for me anyway though he wasn't concerned with it as a stand-alone number)...stopped the Cal/Mag and the headache stopped and BP went back to normal and continued to be normal for duration of pg. We think I'm just really sensitive to that form of cal/mag...anyway, just a consideration if you may have changed anything in your dietary/supplement/med regimen.