I do accounting (bookkeeping) and HR at a college. There's a fair amount of people interaction, and I'm ok with it. Only time I really have trouble at work is if I have to deal with "conflict" and sometimes if I have to ask for stuff. I hate making phone calls. I spend a lot of time researching stuff on websites so I don't have to get the info directly from another human.
My bigger problem is personal relationships. I can handle professional contact with people pretty much but on a personal level, there's much more anxiety, avoidance and general cluelessness about how it's supposed to be done. I've got a few close friends and some more casual friends, so I'm not totally alone but I don't feel comfortable calling people to chat--yes, even my own siblings--or to, god forbid, invite them to do stuff. So I end up never doing anything unless someone invites me.
Like you say, when I get depressed, it's REALLY hard to stick to the plan. I think medication will help with that. Do you take any? Ironically, taking my meds is one of the things I'm currently avoiding! I stopped 3 weeks ago even though I know they make me feel better. I can't even tell you why I'm avoiding swallowing one little pill. Every day I say I'm going to start up again but then I don't.