if youre really struggling and want to start over, try easier subjects, as an A* in an easy subject is valued more by unis than a D in a harder subject, unfortunately, because you have to remember most uni courses don't require specific A levels, just grades.
Dont give up, my mum started a business-ish thing by asking her friend to put some of her art in his shop to sell, and she's just made an etsy shop. If you need to, go to pound shops etc, buy your materials, then sell in upper class areas, maybe even getting customers to choose what to pay. If you dont know anyone, just go into a shop and ask if they'll sell your work, they may charge you, but then you can raise your prices.
If you want help starting a business, check out Biggabusiness, I work with their other half, Biggafish, organising events, but it will be good if you need funding and mentoring....