See your doc. Besides the obvious- reduce your stress, make sure you visit your priamry care doctor, to determine if it's more than just a stress ulcer-sometimes, it may represent something more serious like a heart attack.
Reduce stress. Stress isn't good for your stomach or the rest of your body, so it's best to avoid or manage the stress itself. This has been addressed many times on healthtap already, and also may improve with in-person professional help. Meanwhile, antacids or pepto-bismol can soothe the stomach as a stop-gap measure.