FUR LOSS

I hope someone can help me with this. Here are some facts, what i've tried, what i plan on doing and need your feed back :)

Female 7year old black cat
balding in the belly (no signs of redness/irritation/dryness/crusting/scratches/bleeding/bumps or heat)
Cat is acting normal - playful/eating the same/enjoys people
At first i read that mix half of vinegar and half of water to rub on her tummy.
It helped a little she started growing a light fuzz of fur. But the area just kept getting bigger.
Then I bathed her more often- no change
Changed her food/diet- still no change
finally took her to the vet they said it was allergy related it could be food/flea rx/stress. She is completely healthy!
What should i do? I've considered changing her kitty litter and her sleeping area. Also considered giving her vitamin C daily to see if her immune system can help fight what ever this is. I need help...!!
It started shortly after her vet visit last summer August 08- is it possible she could have caught something there?
HHHEEEEEEELLLLPPPP!!

[opus88]

hi...please do not give Vit C without a Vet's permission, I've never heard of using this for pets before so please check!
Also....are you bathing kitty regularly???..............because if you are that maybe the problem, cats don't require baths...it strips their coats of their natural oils and may also be allergic to the shampoo's.
I posted a lengthy answer below this about a cat licking itself and gave some websites to help with some answers maybe you could read that for some other options to try.
good luck and welcome