It may be an infection caused by lax disinfection of injections, or it may be an infection caused by the incomplete absorption of injected drugs in dogs. After receiving parvovirus treatment, my puppy has a similar bag around its neck, which is where doctors give injections. Later, I went to the pet hospital to find a doctor to cut the dog's neck, squeeze out the pus and vegetation from the bag, clean it and sew it up. Your dog's bag is about to burst by itself, which means that this pustule is very mature and can't be delayed any longer. Taking medicine or something can't solve the problem, you must have an operation! If you drag on, it is very likely that the dog will get sepsis, and the baby who has recovered from a serious illness can no longer stand the toss!