Tested positive for morphine?!? Help!!

Okay let me first say I am 100% not a drug user nor have I ever been. I experimented a little in college but never anything hard. I take Zoloft, unisom, b6 and prenatals and that is all. I’m 9 weeks pregnant and just got a call from my OB that I urine tested positive for morphine. I’m freaking out!! They said they were surprised and want to retest me. Has anyone ever had this happen to them??? And did you figure out how it happened?? Please help!!