Is it normal to get drunk after one beer?

Everyone reacts to alcohol differently. Also, it sounds like you are a relatively small person, so one beer does for you what two beers would do for a 200-pounder like me. It's good that you are able to be objective about how you felt "under the influence"...when you STOP recognizing (or caring) what it is doing to you, you are in trouble, so take it slow. You may want to make a habit of alternating between beer and soda or water. Only drink with people who you know to be good friends and take the Designated Driver thing seriously.