I have a very confusing situation. My boyfriend and I have been together over a year. We both had partners before each other, but have always used condoms. Since we have been in this relationship for a year, and have both been tested for STIs, and I am on birth control, we have started to use condoms less. We use them when we remember but if its a spur the moment kind of thing, we don't worry about it.

Recently, my boyfriend approached me and said he has an STI (chlamydia) and I should get tested. I was mortified! I had just been tested two weeks before and everything came back negative. His previous testing had also been all negatives. I went back and was re-tested, and again the results came up negative (I was given a prescription just in case).

Neither of us have ever had sex without a condom before now. How is it possible that he suddenly developed an STI when both of us have tested negative before, and haven't been with anyone else? Could it be a misdiagnoses, or is it possible to get an STI another way? For example, having unprotected sex while the girl is on her period? Help!!