Ha, I know exactly how you feel about going blank, I've been right there.
Let's see, first of all, Celexa should actually be helping with more than your depression. I took the generic version Citalopram for Generalized Anxiety Disorder and Social Anxiety disorder and it helped a lot. SSRIs are often prescribed for anxious disorders. If you feel like it is really having no effect and you've been on it a while, I'd ask for a switch, yes.
Sorry to tell you, but the thing about your sort of anxiety is its gonna take a while-- both agoraphobia and social anxiety are conditioned, meaning that its not just an imbalance of chemicals keeping the fear there, its that those chemicals spent a very long time building up associations between being outside with people and your very strong fear.
I'm kind of not liking the sound of the help you're getting-- they're prescribing you brand names which I always find shady (remember, doctors are required by law to prescribe the generic version if you ask for it), and it doesn't sound like you are getting any therapy to go along with it? The most statistically effective treatment for anxiety is both medication and therapy at once. In fact they make each other much more effective. For anxiety, I like Dialectical Behavior Therapy, or any sort of Behavior Therapy. Try to avoid therapists who just want you to talk about "whatever comes to mind". Though you obviously have a pretty tragic history, I wouldn't suggest focusing on that in therapy-- it really isn't the most useful thing. You just ruminate and possibly make yourself more anxious, and in the meantime waste a lot of money. Behavior therapy should be short term, one session a week for six sessions was what I got, and that should really be all you need to give you the tools to do behavior therapy on yourself. Think of it more as a short course on how anxiety works in your brain, and how you can manipulate it effectively.
Oh that's a good one-- Xbox live is a great way to practice being social-- maybe you can take it in steps, socializing on the internet is easiest, you have time to prepare your statements and think about your answers, and then you can step up to maybe text chatting, and then to voice chatting-- just remember you'll never see that person again, they don't even know who you are, it doesn't matter. Remember not to take negative reactions in socializing too badly-- those are good things, they are teaching you the things you have forgotten or missed about being social. If you don't get negative reactions and people are just too nice and not honest, it's hard to get a feel for socializing again. Something to remember.