skin rash/scab on belly of mini dog

Question
My dog got a weird rash/scab 3 weeks ago.  He eats dry food, gets bath every month, only walks in the neighborhood so on grass or concrete or plays in the backyard. Three weeks ago, I noticed this awful scab (like human scabs dark brownish/black color, feels like a scab, snake skin). The scabs fall off but then starts turning red and spreaded all across his lower belly, and to the left and right of peeing area. Then the rash turns back into a scab again and cycle continues and does not seem to end.

Normally for humans, when you scab it's a sign of healing, when the scab peels off, the wounds have healed and a scar may or may not remain.  But in my dog's case, it seems to go through this weird cycle of rashing, scabbing, rashing, scabbing, and repeat again etc. My dog does not itch, it does not hurt him when I touch the infected area.  I have been taking him to the vet but they have no clue what it is.  They have done a microscopic test and does not appear to be bugs related. He has been put on Prednisone, Cefpodoxime Proxetil, a sorta creme that didn't help, then a spray that smells like alcohol, and some vitamins.  After 3 weeks, this rash/scab is still there.  Everytime, I think it's getting better, the scab disappears but the rash returns and the cycle continues all over again.  DOes this sound familiar? please help. Thank you!

Answer
This is most likely a bacterial infection.  Topical antibiotics do not seem to work well in animals, so a systemic drug, like cephalexin would be better to treat that with.  Ask your vet about infection.  If it itches, then a systemic steroid may be better than a steroid creme.  Your vet can always do a skin biopsy to see if this is a more uncommon problem.