Unprotected sexual intercourse always carries a risk of pregnancy
. If your urine pregnancy test is negative, it is always better to consult a Gynaecologist and get a serum beta HCG
test done and also an ultrasound
scan of the pelvis, to rule out the cause for the missed period.
If you are not pregnant, then you may require progesterone
pills to cause withdrawal bleeding. These are prescription drugs. Please see a gynaecologist before you take them.
Hope I have answered your query.