My employer hasn't paid me overtime in 6 months — what can I do?

This sounds like a misclassification violation of the Fair Labor Standards Act (FLSA). To be exempt from overtime, an employee must pass both a salary test AND a duties test. Loading trucks without supervisory responsibilities almost certainly does not meet the executive, administrative, or professional exemption criteria. You may be owed significant back pay for up to two years (three if the violation was willful). File a complaint with the U.S. Department of Labor's Wage and Hour Division, or consult an employment attorney — FLSA cases are often handled on contingency.