I also agree w/everybody here...talk to your supervisor/mgr about how things are too much.
Say something along the lines like, maybe even suggesting they bring in a part-time office clerk to assist you with some of the work to allow things in the office to run smoother. This shows your taking intiative to the situation and willing to delegate responsibilty to another person. It shows you're company minded too!
It may cost you your job to go to your supervisor and say "you're giving me too much work, I can't handle it!" or something along those lines. At least in my experience, I knew of a fellow co-worker who had this problem, complained everyday, and brought it to her boss's attention. To make a long story short...after she told them she was overloaded, she was discharged shortly after.
You can get your workload down by pointing out how an assistant may be of some help to the company. Maybe you can write an outline of daily duties your assistant or office clerk would do and discuss it with management. If they don't agree, suggest they hire a college student to come in 2-3X a week to help out with some office duties in your department. They wont have to worry about budgetary constraints, since part-timer clerks are paid hourly.
Just my suggestion. Don't quit your job unless you have another one set up and ready to go, otherwise, you loose your income and benefits too. Trust me, being unemployed now, it really sux! I mean, for the first few weeks, it was a nice little vacation. But now, sitting at home, doing nothing but searching for a job and practicing the computer programs, it 's boring. Having no $$ sux too! And, by the way, if you leave your job on your own will; quitting, you don't receive unemployment insurance. So unless you have a good amount of money saved, I would bring that suggestion to management and if things don't change in the next two months, start sending out resumes and head out of there! Good luck!!!