I've been on Clarinex for several years, and it works great for me. I've recently switched to Zyrtec because DH and I are trying to get pregnant and it's a bit safer during pregnancy. I've been having horrible headaches since I started taking the Zyrtec. Is this a common side effect? I thought maybe I wasn't drinking enough water, so I started drinking more during the day. That helped some, but around bedtime every night I get an awful headache.