<s>[INST] Hi doctor, I had sex for the first time. After that, I did not get my periods yet. I went to a gynecologist. She had taken my blood sample and it was negative. But, still I have not gotten my periods and it has been a week ahead. What could be the reason for my late periods? [/INST] Hello. As the serum beta hCG levels are less than 3 mIU/mL, the pregnancy is definitely ruled out. The delay in the menses is mostly due to sex induced stress after the first time when reproductive hormones readjust themselves. The menses can get delayed even up to two weeks, so just wait for another week and they should arrive. If not, then you can safely opt for a progesterone withdrawal to resume menses. For further information consult an obstetrician and gynaecologist online --> </s>