each time an employee took sick leave, resigned or was terminated I was called upon to perform their job functions in addition to my own until someone was hired. I had no formal training in any of these functions. I was an administrative assistant with job functions of a director, accountant, receptionist. Some positions were never filled and remained my responsibility. I had no clerical support while my predecessor did.
I cannot advise you on New Jersey law as I am not licensed in New Jersey. It is possible that New Jersey law differs from federal law and that you may have a valid claim for unpaid overtime pursuant to New Jersey law.
That being said, under federal law, it is possible that your employer is mis-classifying you as exempt from overtime. The law is very complex and fact-specific. Thus, I cannot determine based on the information you have provided whether you are legally entitled to overtime under federal law. However, I will note that the exemptions are construed narrowly against the employer. What matters in determining whether you are, in fact, exempt, is the primary job functions you perform, and not your job title. The work you perform as a receptionist, for example, would not qualify you as exempt unless it was merely incidental to your primary exempt job duties. How much money you are paid is also relevant, as only employees who earn more than $455 a week are exempt under federal law.
You should immediately consult an attorney in New Jersey about this.