Hi and welcome to Yorkie Talk! I'm from Alabama, too. Bless you for rescuing Jaxson!
He's probably just adjusting. How long have you had him now? As you said, no idea what he's been thru in the past so I would think patience and love and understanding are all you can do right now. There is a sticky around here somewhere with advice and tips on working with rescues. I will try to find it and come back and post it for you
Here, this may help:
http://www.yorkietalk.com/forums/yor...free-book.html