Aklein and Calipursegal are giving you some great advice. Your original email was too personal - meaning you didn't specifiy what you have done for the company that merit a raise, but merely the personal reasons in your life why you need it. That won't fly.
To help you gather your reasons as to why you deserve a raise/promotion, list out what you have accomplished (not necessarily what you do), any financial impact (in terms of savings) to the company, and finally ways you are contributing to the department and/or company. Also research what people are currently paying for part time jobs like yours (you can do this by searching careerbuilder/yahoo/ really any job board).
I also agree with Aklein about coming up with a plan B in case your request for a merit increase & benefits are met with a "no". Think of other things that could help you (ex. ask for overtime pay, perhaps no raise but you would take benefits, etc.).
I know all this may seem scary but you can do it! Don't be afraid to ask for what you want.
Good luck