Rivals symptoms and conditions

Taking Z-pak for the second time this week. Each day has gotten worse. I take them at night, figuring that the worst of the effects would be during my sleep. Well, that's not so. Starting about 9am each day, I get horrible dry mouth, chills, and pain in my chest that rivals any pain I've ever felt. I have trouble eating and I feel super weak - including some tingling/pins and needles in my hands and feet. It usually goes away by about 6pm and I start feeling better. I do take my Claritin at about 8am every day. Could there be an interaction? It seems odd that I feel OK on waking up, but feel terrible for hours after taking the Claritin while on the Z-pak. Has anyone ever experienced this? Any advice on how to handle it? I have company in this weekend and I can't even function to entertain them!! Thanks!!