Thanks for your question, my name isXXXXX and hopefully I can be of some assistance.
I'm sorry to hear that your dog is not feeling well, but hopefully there is an underlying condition that can be treated medically.
Based on your description it is likely that your dog is experiencing skin allergies, or canine atopic dermatitis (atopy). This is likely a genetic predisposition of the body to react in a hypersensitive way to substances that would usually be considered harmless, such as grass/tree/weed pollens, house dust mites, flea bites, ect. The immune system reacts abnormally when exposed to these substances in cats/dogs with underlying skin allergies, which causes a mass of histamine and other inflammatory mediators to be released in the skin. This causes a great degree of inflammation and itch (pruritis) in the skin, which dogs and cats react to be licking/grooming excessively and scratching. This can then commonly lead to abrasions and/or infection of the skin.
That being said, for most cats/dog that present to my clinic for the first time with this type of skin disease, I certainly perform a formal workup to rule out any other causes of itchy skin. This would include a check for fleas, other external parasites with skin scrapes, and a fungal culture to screen for ringworm. I sometimes also place them on a hypoallergenic diet for 8 weeks to screen for food allergies.
In the meantime, your veterinarian can probably start your dog on an antihistamine to help with itch. An antihistamine alone, can probably help about 10-20% of dogs with underlying atopy as the cause of their skin infection/itch. This usually doesn't "cure" their allergies, but rather lessens the inflammation and/or makes them not want to itch their skin as much. If you see a decrease in the amount of skin lesions while your dog is on an antihistamine, then it is likely working and you can probably continue to give the medication through the itchy season, or year round if that is the case. For my smaller patients (10-12 lb), I usually recommend the following dose of Diphenhydramine (Benedryl).
Diphenhydramine 25mg - 1/2 tablet by mouth two-three times daily.
I hope this answer was helpful, I wish you and your dog the best.
Positive feedback is much appreciated.