1- I wanted to know if you feel nervous or unconfortable while at your job, because your social anxiety could be related to two things: either you're unconfortable with people - in which case you'd not feel so great at yout job - or you're unconfortable in situations you don't know how to behave or don't have full control of the situation. Since you've told me you've been working there for 8 and a half years, I'd belive the second option is the most probable one.
As for 2 and 3, I can sense you have a tendency to isolate yourself, as you are confortable in your present inconfortability. You are suffering for being away from social events that make you anxious, but it's a suffering you know, a suffering you don't have to share with others, so you choose to be like that. Apart from the professional help I'd recomend you to seek, what I'd ask you: try going out with some friends, including that friend of yours, and just be yourself, don't compare yourself with others because that is always an unfair comparison - everyone is different, and in our minds difference = inferiority, and try not to control what you do and say. You're obviously a smart and articulated person, so you should have no problems there.
About that isolation period of yours, that you're planning: I'm not sure what you're thinking about achieving with that... What will change? Is it only for the stomachache?
And about that, your stomachache, I'd continue seeing a doctor about it, it could be caused by your anxiety, but it could be doing some actual phisical harm. A regular doctor could be able to help you on that.