The rate at which alcohol is metabolized varies between different individuals, based on the activity on specific liver enzymes, hence the difference in alcohol tolerance in terms of getting dizzy, nauseated, tipsy etc. You may also have a "sensitive stomach" whereby the inner linings of your stomach (gastric mucosa) get easily inflamed upon contact with alcohol (gastritis). You are therefore advised not to drink on an empty stomach, and choose alcoholic beverages with a lower alcoholic percentage. You should also get a routine check up by a physician and do a few tests to rule out stomach inflammation, or helicobacter pylori which causes stomach ulcers, and have a baseline liver enzymes levels taken.