Puppy Rashes Skin

PUG PUPPY! Skin problem? Please help! Any suggestions welcome …?
My pug puppy who is 3 months began receiving little impact 'on top of the head about 2 weeks ago. I thought the bumps were caused by rough housing with my chihuahua full grown, but has progressed to where it is hours throughout the body! I can not do it in vet until tomorrow, but I'm curious to know if any entity has had a similar experience, are the bumps under the skin and which seems bald area where are … to the point where there is very little hair on top of your head! Has this happened to anyone elses DOG! 'm Really freakedout …. also does not seem to be a rash contagious because my chihuahua has been able to do anything like this! Welcome all the answers!
I would recommend you have your veterinarian do a skin scraping on areas that are affected. In a dog of this age, demodectic mange is not uncommon. It causes hair to fall, and causes a rash. It is usually not itchy. The only way to find this is to perform a skin scraping that can cause additional redness. Other possibilities, like a simple bacterial infection of the skin, parasites of the skin, or allergies, but these are not so common. Ask for these when you go to the vet and see what is recommended. Most of these conditions are easily treatable. Good luck!