Under the Fair Labor Standards Act (FLSA), you are owed 1 1/2 times your regular rate for your overtime hours. I'm not sure what the "paper" is you say he made you sign each week. But overtime is required by law, and an attempt by the employer to get you to waive that right by signing something is probably not valid. So based on what you've said, I believe you may have a very good claim for overtime pay. You will, however, have to be able to prove that you actually worked overtime hours. Do you have timesheets or other records showing you worked over 40 hours each week? Does the paperwork you signed each week say you didn't work more than 40, and even if it does did your employer know that you worked over 40 but told you to sign it anyway? The answer to those questions will affect whether you can prove to a court you actually worked overtime.
Second, you can go back 2 years on the seeking past due overtime, and up to 3 years if they acted "willfully" refused top pay overtime. If you're already at 2 1/2 years, then the clock is running so the sooner you seek legal representation or take legal action the better you will be able to preserve your full rights to past due overtime.
Third, threatening to withhold your paycheck or to give you a bad reference because of your demand to be paid overtime that is due you may be unlawful retalation under the FLSA.
You may want to consult an employment lawyer, and/or contact the Department of Labor Wage & Hour Division (they have a Dallas office. the number is (817) 861-2150).
This information is provided as a general reference based on the limited information that was provided and should not be considered legal advice. Providing this information does not create an attorney-client relationship.