I'm guessing you mean that you get paid twice a month, like on the 15th and the last day of the month. That's semimonthly. Bimonthly would be every two months, biweekly is every two weeks.
Read the following article from a CPA about how that's calculated.
http://www.kempercpa.com/email/2012/...culations.html
As far as I know the calculations for overtime must be based on your current hourly wage and not prior year salary.
I think you are being scammed by your employer and stroked with this "it's the law" business.
I suggest you either pin them down and insist they give you the statute number so you can look it up or just contact your state's regulatory agency and file a wage claim:
http://www.illinois.gov/idol/FAQs/Pa...aring-faq.aspx

