cat chewing hair off

Question
Hello we have 2 cats, the younger male about 6 months ago began going bald around the base of his tail. We took him in the vet did urinalysis and said ( steyvesite)? crystals in the bladder. He was on special food for a month without much change. He got even worse. He has been back again different Dr. same ofice insist it was flea allergy- gave shot (last 2 weeks) 2nd shot for instant relief. It worked for about a week we went back after 2 weeks the original Dr. looked again and said Anxiety- since the hair was now missing at the inner front legs. He is now on Amytriptyline I believe.
Well our older cat has since started chewing herself and leaving little scabs and is starting to go bald.  Do you have any suggestions?.

We built a new addition on the house April till now.

They did get into attic space a few times during it above old house and on insulation..

Our eldest dog passed away Last Fathers Day :(

We had a baby 6 months ago.
Thank you in advance for your time and any ideas you might have.
Sincerely Josh Thelen


Answer
When cats are chewing or have hair loss, we first think of allergies.  The shot may have helped because is was a steroid.  You can get these DepoMedrol shots every month to 6 weeks if they help stop the allergic signs.  The amitriptyline may stop itching as well. Another drug that is helpful in itchy cats is chlorpheniramine.