From the little details you've provided, it sounds as if you're implying you have had drinks before and your stomach is upset possibly from it. Are you hung over? How often do you drink? What do you drink? Do you eat anything prior and during?
If you have noticed your stomach reacting poorly to alcohol, don't drink it. But, if you really really want to at the party, try red wine or a really light beer. If you're only into liquor, what ever your choice is...cut it in half (not 4 shots to 2, but 1 shot to 1/2 in a mixed drink) and stay away from straight shots.
By the way, if your stomach starts hurting while drinking or just after you may have a stomach condition that needs to be treated by a doctor and alcohol is doing more damage.
We disregard the simple fact: if something hurts, something is wrong.
Also stress + alcohol can = ulcers