My dog had a large pimple like thing on his back. I popped it and a bunch of thick white stuff as well as blood came out. Now there is a hole about the size of a BB on his back. He scratches his skin a lot, and sheds. What is it?

The white discharge is pus made of dead skin/tissues cells. If your dog is showing signs of discomfort, then keep an eye on him.

You may also want to keep the injury clean (wash it out regularly with hot water) and ensure it remains dry at all times! (pat it dry gently)

What you want to watch out for is if the wound (that's essentially what the bb size hole is) becomes hot, swollen, or inflamed.

If it does, then this could be signs of an infection which you will need a vet to deal with.