There are certain strains of weed that have a powerful calming effect that also help depression. I believe the "Strawberry Cough" strain is one of the best for that sort of thing. Research strains, chances are you'll find one to fit your needs.

Xanax can be good for temporary relief of stress an anxiety, but taking it for long periods of time can create a horrible dependency on it. There's a reason doctor's don't like to prescribe it, it's highly addictive and has a lot of "potential abuse" qualities. If you can, I'd recommend getting off the Xanax as soon as possible.

I'd recommend finding a therapist to talk to. The VA would definitely help you there. While it's tempting to control your symptoms with pills, I think talking out your demons would help. That's just my two cents, just a suggestion. It's hard to talk about shit, especially horrendous and life-altering shit, but if you don't talk about it it eats your insides. If you DO go to a therapist, be open and up front about your marijuana use. You'd be surprised. Make sure you're going to a THERAPIST and not a PSYCHIATRIST. The psych'll dope you up so fast ...

Weed is a wonderful thing, and I hope it's helping you. It's certainly better for you (mentally and physically) than the Xanax. Just hang in there, that's all any of us can do.