I Feel Stupid

So today I went to my first class of math and I had a really hard time understanding what the teacher was talking about. Well I kinda knew what she was talking about but I'm not as fast as all the other students when it comes to figuring out a problem. It's been 2 years since I've been to school and I feel like such an amateur right now. Is this normal? My brain feels so rusty. And my attention span sucks too (probably due to all that drinking I used to do).....Am I screwed? My focus just really sucks....I get distracted too easily. Do I have some kind of brain disorder? I hope I'm just feeling this way because it's been a while since I've actually done a math problem. I honestly haven't done jack $hit since I graduated high school. I took 2 years off to work on my people skills as a cashier and I'm fine now but I'm slacking with school. I don't feel welcomed at a place like school, smart kids go to college and apparently I suck at it. I feel like really unique but in the bad way...I feel like all the other people now know how dumb I am. Should I just go on a marathon of studying?