It sounds like your dog has a bacterial and/or yeast skin infection. This can be due to allergies or an endocrine disease like Cushing's or a low thyroid.
Episooth is a fine shampoo, but if there is a skin infection, then a medicated shampoo containing chlorhexiderm and either ketoconazole or miconazole will be better. I recommend lathering the dog up and leaving the lather on for a good 10 min before rinsing it off and bathing the dog twice a week.
But a skin infection requires antibiotics. If the fur/skin feels somewhat greasy or has a "funky" smell, then yeast is also present and an antifungal medication (like ketoconazole), would also be prescribed.
Was a thyroid panel done on your dog or just a T4 level with other bloodwork? Some dogs have a low normal T4 level, but their Free T4 and TSH levels are abnormal, indicating hypothyroidism. Since everything seemed normal in August, I would do a thyroid panel to make sure that isn't the problem. Hypothyroid dogs often have skin infections that aren't itchy.
I would definitely get Tater Tot back in for a recheck. If your vet doesn't think it is a skin infection, then a skin biopsy could be worthwhile.