"Hot spots" happen when the skin is abraded (it can even be something as small as a tick bite that causes the skin to open). When the skin is abraded and it then gets wet from licking or swimming, etc, bacteria is introduced because of the moisture and this causes the hot spot.
The best thing for a hot spot or bacterial problems is to wash the area well with peroxide and then shave all the hair away from the sore. Hair traps moisture and you don't want that. Then dry the area completely and apply some neosporine ointment. Distract the dog for 5 minutes and then he can lick it. But most dogs won't because it tastes terrible.
If this doesn't help, you will need to see the vet to be sure it IS a hot spot and to get possible antibiotics.
The most common cause of these crazy skin problems is allergies, especially with some breeds. These allergies could be from grass, contact with a cleaner or chemical or could even be food related. The allergy part is sometimes tough to treat but there are some simple things that you can do.
When the dog abrades the skin by chewing and scratching, this opens up the body to infection. Many dogs need antibiotics because of this.
See the vet so that they can get the dog started on antibiotics if you suspect this.
Many dogs also need a shot of prednisone to control the itch and give the skin time to heal.
The only thing that will give her immediate relief is the benadryl.
I hope this helps!
Let me know if you still have questions.
Yes. Those are typical "hot spots" (or at least that's what it sounds like since I can't see them).
These skin problems usually have an underlying cause of allergies.
If he's eating well, drinking, normal activity level, etc, you can probably wait to see the vet until tomorrow. But go sooner if you still have concerns.
You are very welcome! Let me know if you have further questions.