WA Labor & Industries has much information available at its website. The page for information on overtime is here: http://www.lni.wa.gov/WorkplaceRights/Wages/Overtime/default.asp .
The employees at L&I will be able to tell you whether overtime must be paid in your type of work. The contact information is available through the above site.
Alternatively, you can review your facts and options with an attorney.Ask a similar question