Probably genetic, especially if you are not Caucasian.
Everyone has 2 copies of the ALDH2 gene that is responsible for producing the enzyme that decomposes alcohol, but some people have 1 defective copy, and some people have 2 defective copies.
People with 2 working copies can drink all day. People with 1 working copy can drink moderately, but will have mild flush reaction, and definitely can't drink as much as people with 2 working copies. People with 0 working copies will feel very uncomfortable after having just 1 or 2 drinks, due to acetaldehyde buildup. Usually they aren't drunk (because the actual amount of alcohol consumed is small).
Alcohol first gets converted into acetaldehyde by another enzyme (this most people don't have problem with), and then acetaldehyde gets converted into acetic acid (harmless) by ALDH2.
Acetaldehyde is toxic, and acetaldehyde build up is what's responsible for both flush reaction and nausea, etc.
Judging by your description, unless you are allergic to alcohol (which is totally different and much less common), you probably have 0 working copy of ALDH2.
Most Asians have 0 or 1 working copy, and most Caucasians have 2. Don't know about other races.