My dog is sick....right?

So my little Lasso Apso is really sick. She has this itching/chewing problem. It's horrible. She chews her skin and itches herself constantly to the point where she bleeds. Even when she's bleeding she doesn't stop, so it turns into a pusy, SMELLY, painful (I'm assuming) mess. She has hardly any hair left and smells horrible. It's like she's rotting. It makes me sad to see her hurt. We've tried nearly everything: cones, baby sleepers (to keep her from tearing up her skin), "hot spot", shots from the vet, switching her food...everything. We've spent at least $1,500 at the vet and they still claim they don't know what to do. She's allergic to basically everything, even human skin. HUMAN SKIN!!! I just don't know what to do. She shakes all the time too. It's so sad. It wasn't always like this though. It started after we took her to get trimmed up at PetCo. They burnt her with the shavers and ever since then she's been doing this. What do I do?! Please share anything you think might help.

My dog is sick....right?
Taker her to another vet and get a second opinion.