How can I test positive for Chlamydia when my partner is negative and he's the only one I've been with?

Freaking out. I know it’s curable but I can’t get treated. My parents will fucking hate me if they find out. I’m 18.
He is negative. He worked in a hospital he gets tested regularly. Last time was ¾ months ago-ish and he was negative. Last time we’ve been intimate was 6+ months ago. I can’t call doc until Monday because he’s out. I told him not to send prescription. I can’t be positive if he’s negative, right?