I have a nervous stomach too, and I know how miserable it is- everything turns to sawdust in your mouth, then tries to come back up when you force it down. BLEH.
If you can eliminate the stressor, or find some zen position with whatever is stressing you out, that would obviously be ideal. But don't stress about being too stressed to eat, that's not going to fix anything!
Try to make EVERY calorie you eat count. Snack on yogurt with a high milkfat content, eat lots of nuts and nut butters, eat good oils and things high in natural fats- fish, avocado, etc.
One of the things that worked for me was being really distracted. I'd get a really good book or go and see a movie that looked excellent and I'd make sure I had lots of food with me (yes, I sneak it into the movie theater! Big pockets are a must!) and I'd snack while my brain was focusing on something else. Then I'd look down and realize I'd eaten my entire stash of peanut butter crackers or whatever I had. And after I'd feel remarkably better- I was still stressed, but it wasn't able to tie my stomach up in knots like it did before (because it was too full, haha).
Good luck! As long as this doesn't continue for forever, you're depriving yourself of nutrients but the baby is still getting what s/he needs....just make sure to restock your reserves at some point.