What you are describing at the moment with lumps all over her body sounds a bit like hives. This is an allergic reaction that causes these swellings. It can be to an insect sting, or to a medication. However, you have treated her correctly for this with Benadryl. The usual dose is 1mg per pound every 8 hours, so she could have 2 to 2.5 tablets given every 8 hours. Here is more about Benadryl:
You should see improvement within 30 minutes.
Here is more about allergic reactions in dogs:
The fact that your Pit Bull did NOT respond to the Benadryl suggests, however, that this is not hives, but instead is something called folliculitis, which is an inflammation of the hair follicle. There is even a name for it: "Short coat Folliculitis." Sounds impressive, doesn't it? It is generally caused by a bacterial infection in the hair follicle. These bacteria are just the normal ones that are present on normal skin, but they have invaded into her follicles. Short haired dogs are prone to this.
Now, in terms of what to do about it, I must warn you that it often takes 30 to 60 days on an antibiotic (usually cephalexin) prescribed by your vet to resolve this.
If, however, you want to try to treat this at home first, you could use a benzoyl peroxide shampoo but make sure to condition afterwards (I recommend an oatmeal conditioner). You can get the shampoo at your veterinary hospital, or at a big pet store (PetSmart might have it) or on-line. Try shampoo/condition her once and see if there is any improvement. If there isn't, I suggest you take her to your veterinarian.
I'll give you some links:
About folliculitis: http://www.medi-vet.com/Canine-Pyoderma.html
http://www.peteducation.com/article.cfm?cls=2&cat=1593&articleid=423 (mentioned in the chart)
example of Shampoo: http://www.allivet.com/DermaPet-Benzoyl-Peroxide-Plus-Shampoo-p/26935.htm
example of Conditioner: http://www.calvetsupply.com/index.asp?PageAction=VIEWPROD&ProdID=373
As well as folliculitis it sounds as though your dog has pyoderma - which literally means "pus-skin." A photo would help me to be more certain of this, but from your description I am very suspicious.
Pyoderma is a bacterial skin infection that is seen as red pimple-like lesions usually found in the groin area, and the armpit area. The little red spots may look like tiny pimples and they are filled with bacteria and pus. When they fill up larger they can look like blisters.
There are normally small numbers of bacteria living on the skin surface, but when they invade the skin like this it is called pyoderma. The patch under her neck sounds like "acute moist pyoderma" which is also called a hot spot. You may be able to scrub this area with an antibacterial soap. One example would be chlorhexidine scrub (which you can get at pharmacies off the shelf in Canada and the USA). I suggest people wash small areas of pyoderma 3 times daily for 3 days. Rinse well. Pat dry. Then continue to wash twice daily for 4 more days. Watch VERY closely that there are no more patches coming up.
Because your girl has folliculitis and pyoderma and hot spots (from what you are describing) she will need to go on oral antibiotics to get it under control. Oral antibiotics for skin infections are often given for 2-4 weeks in order to resolve the problem.
Here is more information:
So, please have a look at the links that I have provided. Do the photos shown look like what your dog has?
For tonight, you may be able to give your girl some relief by giving her a COOL bath with an antibacterial scrub from your local pharmacy, followed by a colloidal oatmeal rinse like Aveeno bath treatment: http://www.aveeno.com/productDetail.do?prodid=3662
I do think you are going to have to find a vet tomorrow, as from what you are describing this is progressing too quickly to leave it until Thursday. If your girl is really uncomfortable, you may have to consider an emergency veterinarian tonight!
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Best wishes, Fiona