I need a dr's advise.

I'm on the bc pil kariva and have totally missed my period. My np says since my pregnancy test was negative, continue taking my bc pills and retest in 2 wks. I'm scared I'm doing harm. can you help me figure out when My test could be positive. my periods have been normal for the last 4 yrs on Kariva. Never a problem like this. i was on a lot of antibiotics last month due to a bladder infection and didn't use back-up protection. I've been married to the same man for 14 yrs, so it'd be a pleasant surpeise. I just need to know if the bc pills will do harm if i am?