How come I tested positive for trichimoniasis and my husband tested negitive when I have had no other partners.?

No good test for men. Trichomonas testing for men is tricky. There really is not an effective test for men. In fact, when a female has it, the male sexual partners are generally treated for it and then tested for other STDs like hiv, syphilis, gonorrhea and chlamydia. I highly recommend he be treated since you were positive. A negative male test for trich is not reliable.
Ping pong. Agree with dr. Livingston. "ping pong" infection that can go back and forth unless both partners are treated.
Flase positive. Consider having both you (and your only partner) re-tested. (why were you tested in the first place?).
Trichomonas. Trichomonas can be difficult to diagnose in men. I suggest repeat testing including a microscopic semen analysis by a skilled observer...