Hello, from the history you have given, there are many causes for delayed periods. Since your periods are always regular, apart from pregnancy, stress also delays periods. And also sometimes the urine pregnancy test may show faintly positive line or will not turn out to be positive, this is because of low levels of beta HCG in early weeks.Iin that scenario, you may have to repeat the test after few days or do a serum beta HCG ( blood test ) for confirmation. Hope i was helpful to you.

Hello,

there is no reason for worry, because hormonal fluctuations are one reason for this, especially in young girls within the first few years of menstruating.
Some other reasons which can leaad to this condition are:
Low body weight or excessively losing weight or losing weight quickly can cause you to miss your period. Obesity can also cause changes in your menstrual cycle.
High stress levels can interfere with ovulation and therefore interfere with your regular menstrual cycle. If ovulation is delayed, your period may be late. If you don’t ovulate at all, you may miss your period.
Hormonal contraceptives can cause missed or irregular periods. Some contraceptives, such as Seasonique or Yaz) stop your period for several months or up to a year and others may change your flow so it seems as if you have missed your period.
Strenuous and rigorous exercise can interfere with menstrual cycles. This may be caused by the stress on your body or low body fat.
Some medications will interfere with your menstrual cycle. If you are taking medication, check with your pharmacist to find out if missed periods can be a side effect.
Hypothyroidism, an underactive thyroid, can change how your body produces certain hormones which can cause you to miss a period or to stop altogether.
Just as when you suddenly lose weight or are underweight, eating disorders can interfere with your hormones, causing irregular or missed periods.
If you suddenly switch from day shift to night, or vice versa, or have a job which requires you to continually switch shifts, you may notice a change in your menstrual cycle.


I hope I helped you a little bit, but if your period will not come in a couple of days you can repeat the pregnancy test and if itis negative again than visit your gynecologist in a few weeks if your period won't come or sooner if you are worried.