You're not the first kid to sell lame shirts with designs that have been used before. I'm guessing that your artwork isn't copyright free, so you could get sued for even using the images (except the all text one). Also your use of color is ridiculous ( not everybody wants to be a skittle, bring variety in color schemes). Having a successful business is all about filling a market niche that no one else has. "making cool shirts" is not a good business plan. I understand that this may seem like I'm being an ass, but as far as what I've seen... you're going to spend more money than you make unless some creativity drips out your ass.
I really do hope you come back here and rub it in my face when your a success, but fer serious...