After practicing good oral hygiene practices, including tongue scraping and rinses, you may want to consider other causes for this including dry mouth (possibly from medications) or even gastroesophageal reflux, which can also cause some of thes symptoms
Check out the possibility that the odor might be coming from your tonsils if you still have them. I would try to brush your tongue, if that doesn't help then consult an oral surgeon or ENT doctor.
try brushing back there-- yes, with a toothbrush, or use a tongue scraper for a week or so 3 x per day for a minute or 2 each time. if no improvement, or if you feel there is an abnormal or strangely colored growth back there, then see a dentist.