[gdalton]

I'm not trying to be a dick but this might come across like I am, but here goes.

You and your employer came to an agreement when you started working there, the agreement was obviously for $7.55 an hour, you and he both knew this when you started and you both agreed to it. Now if you want more money from now on then highlight your achievements and press him for more, but do not expect him to pay you more for work that you have already done at the wage you had previously agreed to.
As for others making more money, that is probably because they asked for more to start with, I doubt your boss volunteered to pay anyone more then he could get away with. Then again if you make deliveries and receive tips he could have considered that when he negotiated your wage, as he considered the dishwasher who does not receive tips.
I would suggest that if you like the place stay and negotiate for more money. Believe me it is not worth going to a job you don't like for less then $20 a week after taxes (and that’s if you work full time).
I hope that helps.