Where should I start?

I've done receptionist work for my mother, so I know what the job entails. I feel that I'm just as qualified to do the work as any other entry level receptionist in this field. I have good phone manners, know how to type (though admittedly could use some training for speed), know how to operate most office equipment reasonably well, and pick up new skills very quickly. I've been a waitress for three years, and worked in a retail store call center before, so I'm well informed in how to handle customers. I am still fairly young, and have no college degree, but I feel like if I could just get an interview, I could at least stand a chance of finding employment.

Somehow, though, I can't seem to even get to the interview stage. I've sent resumes and applications to countless places, and have yet to receive one call back. Thinking there was something unimpressive about my resume, I've tried rewriting it over and over, tailoring it to the job I want, and even having a friend of mine, who is a business owner, look at it for mistakes. I don't have a cover letter, could that be the problem?

At this point, I just don't know what else to do. Is it because I don't have any experience listed on my resume? (The receptionist work I did for my mother was when I was still in high school, so I didn't list it for fear of having to explain a massive gap in my work history) I'm considering trying temp agencies and employment agencies, but am a little nervous that I'll find myself disappointed yet again.

What should I do?