Unprotected period sex

My boyfriend and I had unprotected sex while I was on the 2nd day of my period. A few days later he began having symptoms like puss draining from his dick and his dick hurting. He began treating it for a yeast infection with cream but it didn’t go away. About a week and a half later he went to the doctor. The doctor immediately told him he had a UTI, but he didn’t tell him about having unprotected sex on my period. After describing the symptoms the doctor said it sounded like chlamydia and sent him to get tested for STIs. Personally, I consider my genital hygiene to be pretty good and I definitely have not slept around, and I know he isn’t either so I’m a little confused how I would have been able to give him chlamydia. He doesn’t receive the test results for a few days. Has anyone been in a similar predicament?