Mis-classified Job Status

I was hired by a small municipality as a driver. I worked only when my name appeared on the department's schedule. Now I am working 35-40 hours per week and have been for over a year. My classification is "non-scheduled part time" even though my boss puts me on the schedule every day and expects me to be available.. I wonder how it is that I can be classified as unscheduled part time when my name appears on a schedule every day? With this classification I get no sick days, paid holidays, or vacation time, even pro-rated. Employees who are "scheduled part time" get sick, holiday and vacation time. I am scheduled when it is most convenient for my employer and often start work before 7 am or work weekends and evenings, as the need dictates. I am the only worker in this situation. Others in my department tell the boss when they are available. I also do not get overtime (I have to put hours on another day at straight time) I feel the situation is unfair. If I say anything I fear retaliation