No, I would not stop these meds...not at all. Like Lj said, the lethargy isn't likely from these meds...unless her tummy is a bit bothered and it's making her tired from that. But even so, I wouldn't stop the meds for that reason.
Btw, allergies in dogs are rarely helped by Benadryl (have to give 4x a day) or Zyrtec (give once a day).
For more about allergies, read this:
http://www.yorkietalk.com/forums/die...tart-here.html