scratching and biting

Question
I have an 11 year old black cat who recently had a stroke. After recovering I find that he is itching and chewing constantly. Now after about a month my 10 year old German Sheaperd is doing the same thing. I have used flea medications on both but have yet to find one flea on them or their bedding, Or bites on the people who sleep near them. With the Dog she is getting a rash on her belly and open sores from chewing, The cat has white dander when I brush him. The cat has has not hair loss or clumps, The dog however has chewed the hair off her tail but no open sores. Could this be some type of internal problem?.

Answer
If the dog and cat are chewing, it may be that both have allergies.  Fleas are one thing that can cause an allergy, but there are hundreds of other things, too.  The easiest way to see if that is the case is to ask your vet to give each one a steroid shot.  If the itching subsides, then it is most likely allergic skin disease.