I feel drunk all the time and normal when i've drank?

people dont seem to understand/hear me half the time, my words sound slurred and mumbled, can't think of the right words etc. it's been like that since I was a kid. now that I'm older I think the slurring is not so bad but when I do things it seems to lack vividness, I'm always sleepy.
I drink occasionally but not much and when I drink I feel "normal" and can hold normal conversations. I can think and see clearly. For example I am in college went to class after drinking a little bit and I could actually focus and understand what was going on. And when I'd go to speech class without drinking anything I got a C- then I drank a little bit, got a B, then last I got pretty buzzed I got an A on that speech. So is it normal to feel more normal and focused after drinking, and to feel drunk when not?