I tested positive for trichomoniasis but my husband didn't how is that possible?

A positive test for trichomonas (usually by a "wet smear" which shows live trichomonas under the microscope) may be negative for a particular time, but a repeat test is justified to discover a need for treatment of all partners involved.

Trichomonas is sexually transmitted, but it also can be carried for years before being diagnosed. It also clears up on its own in men, without treatment. Either you or your husband may have been infected in past years with it only now being detected. Have a sensitive discussion with your husband, but you can believe him if he says he has had no other partners recently.