I think a lot of your D problem has to do with stress. I always freak out when I have to do something new. When do you actually start your new job? The anti-anxiety meds might be something to check into if you have time before you start. A quick working one is Xanax but it would be a good idea to take it for a couple of days before you started working just to make sure it agrees with you. It helpes me through panic attacks but I only take it once in a while....it can be addicting. Ask your doctor what he thinks???
Otherwise, I don't know what else to tell you except to eat especially non-triggering foods and try to chill out and take immodium.