What Is The Medicine To Get Periods?

hello doctor

im 22 years old

til now had regular periods

my last period was on oct 14, 2013

after that i had sex with my husband on nov 8, 2013 with protection

after that i misd my periods

i had pregnancy test on nov 20, 2013

and on dec 8, 2013 both the times result was negativ

ive gone through thyroid test and hormone test

both are normal

pl suggest me a medicine to get my periods