Overtime: You are entitled to overtime in most cases
You knew you were staying late for work a lot, but when you got your paycheck, it didn't reflect much of a difference from your usual payment. You thought that maybe the overtime would be on the next paycheck and that you were confused on the dates. Instead, your next paycheck came with no difference.
You highly suspect that your employer is not allowing you to stay clocked in the extra hours, even though he's the one who has asked you to stay late to finish work. Fortunately for you, this is not legal, and it's your right to pursue compensation for the time you spent at work.
Overtime in California
According to the law, Californian employers have to pay overtime even if it was not authorized. Overtime is paid at a rate of 1.5 times the employee's hourly rate of pay for all time spent at work longer than eight hours and up to 12 hours a day. Additionally, the employer must pay overtime for the initial eight hours you work on the seventh consecutive day of the week.
For employees who stay on the job for longer than 12 hours (a half day) in one day, the employer must pay double the rate of pay. Additionally, the employer has to pay you double time if you work seven days in a row and over eight hours on the seventh day. If you are not permitted to work overtime, your employer may penalize you or discipline you, but he or she still has to pay for your time.
Salary and overtime
Even if you're a salaried employee, you may be entitled to overtime. Unless the employer can prove that you are exempt from overtime by meeting the exempt status as set by the federal and state laws, you will still receive overtime pay.
You can speak with your attorney if you believe that your employer is not paying the overtime you're owed. If that's the case, you can take your employer to court to seek compensation.