Thinking about going back to school but don't know what I want to do with my life. Anyone care to give me insight/something to think about?

Greetings fellow Redditors,

So I've come to the solid conclusion that I would like to go back to school.

I'm a high school graduate, as well as a holder of a college certificate in automotive service. I'm not a licensed mechanic, but I am/was working towards it. Right now I'm working at a general repairs/tire & lube shop, previously working at a big-name retail store/auto service department. For those living in Canada, you can probably guess where that was.

I've worked in the auto service industry for a good four-and-a-half, coming on five years and realistically, I'm fed up with it. I'm tired of the auto shop drama between coworkers (horseplay), I'm tired of the long hours, measly wage, busting balls, and management/owner who really doesn't care about customer satisfaction (as much as he says he does), when it's obvious he's in there for the 'get it in, upsell upsell upsell, get it out' agenda. I'm for the customer, and I just hate seeing this happen day in day out. I know the shop needs to make money to stay afloat and pay my checks, but this isn't the kind of job I want to be affiliated with. I'm absolutely tired of the automotive industry's blatant crookery. Of course, there are decent shops out there, but I'm no longer interested in searching for them, nor am I interested in degrading my body for a measly pay. Sure I can bust balls even more and become a licensed technician, but I really have no more passion when it comes to this trade.

I was thinking about going to school for business; taking my automotive experience and doing something with it such as opening my own business, but I don't want to end up like other shops. I know if I do things honestly, I'm sure the business will sink.

It's unfortunate (in my opinion) that all I know is cars, but at the same time I was really big into art when I was younger. I wanted to be a designer, a guy who draws/sketches up ideas, makes models, etc., and eventually collaborate with others and end up designing say the next generation Honda Civic per say. But I have no clue where to go about, or even who to ask.

Personality-wise, I'm rather introverted and would prefer to work quietly and by myself. When I'm surrounded by other people and their banter, I don't really get distracted, I just get annoyed. I prefer peace and quiet. Care to recommend any careers that would be suited to my personality? Yes I understand outgoingness, working in groups, and knowing many people are assets to finding a good job, but please work with me.

Education-wise, I'm an average student, took all the sciences except biology though, I've kicked myself in the ass several times for missing that. I'm mainly a college-bound student, I'm not at the level of intelligence, nor credentials to make it into any university.

I'm open to anything, even if it doesn't involve anything related to the automotive field.

TL;DR

I want to go back to school (college), but I don't know what to do. Just give me suggestions, or tell me about your schooling/career search and get my mind going. I'm open to anything.