honestly with that many hives and other symptoms I think I would at least consider the food. you dont even have to stop feeding it but find something to mix in with it like natural balance has several limited ingredient foods that you can mix 1/2 and 1/2 with the natures logic for several days to see if there is any improvement. if so then you know. if not then ok you can see what else to do. like detergent some dogs are allergic to certain detergents. One lady kept a journal to narrow down what it was her dog was allergic to. I havent used zyrtec myself but there are those that have here with good results. Maybe just use benadryl morning and night and see if hes better. Is the pollen count there high? try and think if anything is different. did you put bug stuff on the yard. one ladys dog was allergic to the beef in her heartworm meds. I hope she gets better soon 
