I would take a test if I were you-that way you'll know for sure. If you're already late, a test should show the correct result, and then you can stop worrying whether you are or aren't.
As far as needing to take time off from your job, just tell them that you have a Dr. Appointment and need to head out early. If they ask WHY, tell them you have this explosive diarrhea that comes at the most inopportune times
I think that will teach them NOT to ask personal questions! (Or, you could just say that you think you have an ear infection, or that you have a routine dental cleaning. They don't need to know.)