This is Dr. Christian. Because it improved on steroids it is almost certainly allergies that are causing the problem. Allergies can occur to anything in the environment (food, dust, pollen, grass, trees, cats, etc.). Unfortunately, these allergies can occur at any age and can be difficult to determine what they are allergic to without testing. In most cases medications are necessary to control the symptoms so that infection and hair loss does not occur. Even food allergies are still possible if you have not tried a prescription food. Over the counter brands commonly have the same ingredients and therefore if your cat is allergic to one of those he will still itch. Here are some thoughts:
Allergy testing can be done to determine what exactly he is allergic to and then a series of shots can be given over a period of months to reduce the severity of his allergies. While a little more costly (you can check with your vet about the cost) in the long run it is safer than steroids and can be very effective. I once had a cat that was allergic to mice plus about 20 other things. The allergy shots did well for him.
Steroid Injections (prednisone) from your vet may be necessary for temporary relief. Long term steroids can be detrimental so you want to use this as little as possible.
Unfortunately, other than diet, there is not much to be done at home because antihistamines do not help cats much. I would start with a prescription diet if you have not done that already and then talk to your vet about allergy testing. If you don't want to do allergy testing then steroids can get him some relief while the diet starts to work. If you have allergy testing done he can't have the steroids because it ruins the testing.
I have tried the science diet z/d and it didn`t work. I also bought other special foods like the science diet without the whey,chicken and other ingredients. He is a very picky eater. I have had him for 2yrs and he has never wanted treats or can food. Is there any cremes like destin or i can put on his bottom or bloody sores? just until i get him to vet Monday? thanks,Jennifer