First, until you are age 18, child support (even though paid for your benefit) legally belongs to your mother (even if you are not living in her household).
Second, child support comes to an end when you cease being a child and become legally an adult at age 18.
Third, once you attain age 18, if you qualify as a "child attending school" as defined under Oregon law, the support money becomes payable to you rather than to your mother. You should contact your local Child Support Enforcement Agency to make sure they know where to send the check.