First I amd sorry you and your kitty seem to be going through so much. I suggest you check to see if you have a mobile vet...that might help with the cats stress involving the vet. If not, well, drugs are better than the alternative.
It sounds like it could be a food allergy since it started with her rear end area and is involving the tummy, however it could also be what they call a "hot spot" which increases in size rapidly and is an infection of the skin - either way - she needs to go back to the vet to determine if she needs to be on an antihistamine, some cortisone and or get tested for allergies.
Just to rule out things - have you used any new carpet cleaner, furniture cleaner, new laundry detergent or put down any herbicides, insecticides or pesticides in the yard at all??

You might want to do some research into Diatomaceous Earth. I know quite a few people have posted what good results they have seen with their pets health problems once they start feeding them DE. I have started my gang and myself on it, but it's only been about 2 weeks.

Our house is all hardwood floors. We only have some small areas of carpet rugs, which we have had for over a year. The cats do love to lay on those... I don't know if that could be the cause? If so, would it be likely that our other cat would be having a similar issue though if from carpet rugs?

Is it common for these areas (Tail, Hind Legs, and Stomach) to be affected first with food allergy? I checked my notebook where we keep track of anything usual or changes (we take this to the vet with us each year) and we changed their food brand entirely in January of this year. However, I do think the fur loss on the tail began before that. I am unsure of the stomach/legs, but know it has been within the past year.

I have not heard of Diatomaceous Earth, but will check it out. Originally my cat ate Iams, which we switched a few years ago after the pet food scares. After that she was eating Innova, mostly dry with some canned wet food. We increased the amount of wet food this past year after she had issues with constipation.

We had changed vets, due to being unhappy and getting mixed recommendations from the vet we had, and the new vet thought her vomiting and constipation could be a food allergy. We switched the cats from Innova to Wellness early this year. They do the Salmon based dry food, and they share a pouch of wet food each day. (April seems to prefer the gravy rather than the canned food.) We have had almost no vomiting since making the switch, and no known issued with constipation, but of course now we have the fur loss which is what brought me here.

I THINK the fur loss started while still on Innova... but not positive. However, she at Innova for about 3 years and the fur loss and excessive vomiting did not begin until we moved.

Allergies are very likely, and flea allergies are by far the most common cause of this sort of hair loss, but sometimes no specific cause can be identified. But still, treating for fleas first is prudent. Unless your cat is actually vomiting from the excessive hair ingestion (as that is most likely where the hair is going), you don't necessarily have to treat hair loss. I have seen hundreds and hundreds of cases like this and almost all are either fleas or seasonal. Food allergies do not tend to be seasonal (unless you are changing the diet every season). So I doubt that too many of these are due to food allergies. Most are fleas, and by far the second most common are other environmental allergens (pollens, housedust mites... which are also somewhat seasonal, etc.). But, if your kitty has eaten so much hair that she is vomiting or having diarrhea, then you may need to treat her allergy as well as treat for fleas. I am sure allergy treatment has been discussed elsewhere before, but antihistamines, fatty acid supplements or cortisone are all somewhat effective in treating these situations. Food allergies, when they do occur, tend to be a lot less responsive to routine allergy treatments, so that might be your clue that this is a food allergy if you get that far.

One of our cats pulls out tufts of hair on her thighs, legs, stomach. She would probably do her tail if she could reach it. (She's a little pudgy) It is seasonal allergies. Right now she is on prednizone, and in process of weaning off. We have had a vicious allergy season here in SC. I am still suffering from it as well. And I take Allegra every day, year round.

Thanks for all the replies. Over the past couple of days, there seem to be more vomiting/hairballs. Although I can't be certain which cat its from... I suspect its the one with the almost bald tail and tummy!!!

My cats are given Revolution as a flea/tick prevention monthly. She just had a vet visit a few weeks ago, and they didn't see any fleas on her at that time. Since this has been going on for awhile, I do not think it is likely a reaction to fleas.

I checked with our current vet. Based on her history and current situation, he also feels that it is most likely either a food allergy or seasonal allergy. However, based on the timeline, he thinks it is more likely a food related problem. We are putting the cats on a hypo-allergenic diet to see what happens. He said it may take up to 4 months to notice a difference. If this doesn't seem to help, he wants to look into allergy testing in the fall, but said he would rather try the food first because allergy testing is $$$.

I have a couple of insights I can add. I have a small dog who has similar itching and hair loss problems. With him it has turned out to be seasonal allergies. This spring we started him on Atopica, which is a pet medication that targets allergies. Last summer I spent the whole season bathing him twice a week in shampoo he had to sit in for 15 minutes at a time, and still watched him be miserable the whole summer. The generic Atopica costs about $35 a month and so far it has worked wonders. Not sure if it's a medication you can give cats, but you could ask about it.

Another thing you can do which is much cheaper and more holistic is to buy some salmon oil and put it on the cats' food. Most of them love it and it helps with skin and coat. If it is seasonal allergies with your kitties it might not cure the problem, but it will help soothe her skin and coat while you're figuring it out. I suggest getting a cold pressed salmon oil online from a reputable source so you know it doesn't have any mercury or contaiminants in it. Do a Google search. Good luck to you and the kitty!