Possibilities of false positive Chlamydia test

I went to my gyno in May/2009 and as a routine she likes to check for STD's and everything came back negative. I went again in Aug/2009 because I started bleeding one week before my period was to start and I had some abnominal pain. I tested positive for chlamydia, but when my husband when to get tested his results came back negative. How is this possible? We have been having intercourse. Perhaps we have not had intercoursin the two weeks before because we have opposite shifts at work.What should I do? He blames me and I understand why but I have not been unfaithful and why is his test coming up nagative when we have had intercourse?