Let me ask a few questions:
1. How old is your dog?
2. What breed?
3. How long has the sore been there?
4. Is there a bald spot, too?
5. Did something happen to cause it?
Dr. Debbie
It sounds like a bacterial dermatitis, sometimes called a "hot spot". It will be important to remove the hair off of the sore - shaving it, and as you did - clean it with antibacterial soap and water. You can buy an antibiotic spray to put on it three times daily - with gentacin, an antibiotic as the ingredient. I think you can get this over the counter at a veterinary clinic or a pet store.
If it doesn't start to shrink and dry up in at the most 2 days after treatment is started and it is cleaned up very well - then I would get in to your vet. If you don't think you can shave it, then I would see your vet - because that is important in the treatment of the problem.
Veterinarian
Full time practicing companion and exotic animal veterinarian