What Would Cause Delay In Periods?

hi doctor,
i am not getting my periods. my due date was 1 december. i checked at home twice but result was negative. i also went foe blood test as per doctor advice but it is also negative. doctor has given me medicine names "sysron" and "eldervit-zc". she has said me to take these medicines for 10 days and after that if i dont get my periods then i will have to do pregnency test again. can u tell me if t do not get my periods in 10 days, will there be a possibility of being pregnent.