Hi Myra,
I must first caution you to never use any over-the-counter medications on your pet without talking to your veterinarian first. That being said, it sounds like Little Man could be having a taste reaction or reacting adversely to the Benadryl. Whining and crying at night could be a sign of multiple problems including hyperthyroidism, high blood pressure, blindness, and senior cognitive (brain) changes and I would highly suggest a thorough evaluation by your veterinarian.
All the best,
Dr. Ryan Llera