Sudden low alcohol intolerance?

the first time i ever drank was about four months ago. i remember that night vividly. i drank 10 beers without any problem(at least while i was drinking them). and i smoked a bit of marijuana. in the morning i threw up two times, but it wasn't that bad. it wasn't really unexpected for me because it was the first time i had ever been wasted. but the next time i wanted to drink, which was about a week later, i opened a beer, took a sip and the taste of the beer made me gag. i could barely finish one can of bud light. after i got a little high, i drank like two more beers and i was fine. but that was all i can handle. only three beers! why could i drink 10 the first time, but barely 3 the next? two nights ago i drank again. the first beer went down easier. and i was getting drunk from the second. i ended up only drinking 3. i couldn't drink anymore. i smoked quite a bit and got a terrible headache and went to sleep. i have a condition called gilbert's syndrome, one possible symptom is alcohol intolerance, but how could that be? i drank 10 drinks my first time, without any problems. now i can barely drink 3.