I tested positive as well. I know i should stay off the internet when it comes to medical questions but couldn't help myself on this one.
Not Sexually transmitted (that I know of) and yes, you can test positive with one pregnsncy and negative with Thr other....even test neg. In early pregnancy and pos. Towards the end. That's why they wait until 36-38 weeks to swab. Its such a weird thing, stay off Thr internet, it will just scare you. I tested positive dangit :( so antibiotics during labor it is!