ASSUMING a 28 day cycle, your period is late. Stress and hormonal imbalances can cause this. Take a PREGNANCY test to be sure. If negative, wait a few more days and test again. If it remains negative, see your doctor... They will check for underlying conditions that can cause a missed period such as POLYCYSTIC ovary syndrome (PCOS) or THYROID issues...

irregular periods are common and can be caused by stress . A healthy diet and exercise can help regulate periods . hormonal imbalances or certain medications can also affect periods .If you are concerned, speak to your DOCTOR. 

Normally, the first ultrasound is done around the 6th to 9th week of the pregnancy. This is done to check the growth of the baby and to make sure that the heartbeat is normal and everything is fine. Moreover, it also provides the information concerning the expected date of delivery. Thus, if you experience any symptoms such as bleeding or pain, or if the doctor wants to check if the baby is healthy, they may recommend doing an ultrasound earlier.

Variant reasons can come up with missing menstruation, like stress, fluctuations in weight, or hormonal deficiencies that cause it. If you haven't had your period, try to watch for other symptoms that may have come along with it, such as headaches or mood swings. If you worry, it's better to go and talk to someone you feel secure with, such as a parent or school nurse, who can then show you what to do to be of better help to yourself.