relearning guitar

I've been playing off and on for most of my life roughly 19 years I can play just about anything with a little practice I can get it down. But that's just it I can play others music I feel as if I need to just start all over again I know nothing about music theory and very few scales I'm just hoping someone can point me in the right direction I want to know every thing there is to know about playing maybe a specific book or what not if anyone can help I would greatly appreciate it.