Instead of Benedryl my vet recommends Zyrtech since it lasts longer and doesn't seem to make the animals loopy.  I give both of mine Zyrtech 1x a day.  Mine are 60#'s and 80#'s and get 1 pill a day.  If it's smaller house dog (25#'s or less I'd go with 1/2 a pill a day.)

Have you switched food or where are the treats made?  Mine only get made in the USA treats and dog food.  You may want to switch over to a grain free food or have you had the carpets cleaned lately or new furniture or something different along those lines?