I find it a little weird and astonishing. I think you should buy a lottery ticket as you seem to be very lucky or unlucky in this case. In my 25 years of punting, I have never caught an STI and the chances of catching it through OWO are extremely slim. Nevertheless, it can happen as people have said.
In my experience, Women in general do not like criticism and if you tell them that you may have caught something from them (even a cold) be ready to have shields on full alert.
Like others have said, you cannot prove where you caught it, so my advice would be to go to a clinic, get cleared up, and move on.