Why after I give my digs a bath the next day they have this brown crust on their backs and are full of fleas again? Plz help ?

The house is not the only problem, you also need to spray everywhere outside to get rid of the flea infestation.  If you don't get rid of the infestation you won't ever be free of fleas.  You would have to use your spray every two weeks for 6 to 8 weeks to get rid of the fleas.  You have to get rid of the flea problem before your dogs stops picking them up.

You can do all kinds of things that won't help at all until the infestation is gone.  Bathing only kills the fleas that are on the dog.  Don't need flea shampoo, just a dish soap bath will kill the fleas on your dog but you will just be putting him back into the infestation to just pick up more.

With a bad infestation it may be much easier to hire an exterminator to get rid of the fleas.  He too will need to spray every two weeks for 6 to 8 weeks to kill of all the life cycles of the flea.  Nothing you can do until the infestation is gone.

I live in Florida and have the same problem, although the crust is on the front of my dogs paws.  I don't think the crust is related to the fleas population explosion.

It's sad that all the vets want to do these days is just give vaccinations while you wait outside the building.  I'm not wasting my money taking my dog to a "vet" who doesn't want you in the examination room.

 Because you are bathing them far far too often obviously when you have washed all of the remaining skin oils away; Then their skin   will begin to  itch crack and flake  away causing them to scratch more and self inflict light skin damage  which in turn leads to more scratching problems. And snowballs

Take the dog to a vet along with the container from the store bought junk that you have already applied so the vet can read which poisons in what concentrations the dog has already experienced and absorbed.

You see flea treatments are toxic to both the dog and the flea,,,, Hence they are given or applied taking the dogs exact bodyweight into consideration.

Also any vet worth his while will know exactly  which product. is the most effective against his local flea population and also which poisons his local flea population have become resistant to.

As  fleas develop an immunity to the poisons that have previously killed them  very quickly.

Hence you should never apply store bought flea cures that very often dont work though leave toxic ingredients within the dogs hair, coat, and skin.

My first suggestion would be to get flea & tick medication from your veterinarian.  Fleas can be tough to eliminate the old fashioned way.