There could be a complete absence of bleeding, called amenorrhea. In this post, I will only talk about the absence of menstruation. Then in another post, I will talk about abnormal bleeding (abnormal bleeding could be in the frequency, duration and the amount). You can skip to the paragraph that highlights your concern by looking at the bold writing of the first line.

My daughter is 15 years of age and has not had her period and looks to have developed breasts, armpit hair, and pubic hair.
Your daughter seems to have primary amenorrhea. Make an appointment with their primary care physician, pediatrician or OB/GYN specialist.

My daughter is 13 years of age and does not have signs of breast development, armpit hair, pubic hair nor her menstrual cycle.
Your daughter seems to have primary amenorrhea. Make an appointment with their primary care physician, pediatrician or OB/GYN specialist.

I haven’t menstruated regularly for the past 3 months and I usually have regular cycles!!! (or) I haven’t menstruated for the past 6 months and I usually have irregular cycles!!
This is secondary amenorrhea. You have had a menstrual cycle before, but now it doesn’t seem to be occurring. Usually, it is due to pregnancy. Grab a pregnancy test or go to your doctor and see if you are pregnant. The chances that an absence of menstrual cycle is caused by something other than pregnancy is 5% or less in these situations. If you have noticed that your breasts are fuller, you have gained weight and you feel nausea and possibly been vomiting lately, then this suggests you may be pregnant. You will need to have this confirmed with a pregnancy test which checks your level of hCG in your urine or in your blood.

You are not pregnant and are not having your periods (look above for timeline).
You need to be evaluated further by your doctor. Your doctor will do further tests to see why you aren’t getting your period. They will check your FSH, LH and prolactin levels in your blood to see if that tells a story about why you aren’t having your normal menstrual cycle. If you have low levels of FSH and LH levels, this may indicate you have a decrease in the production of these sex hormones, possibly due to your hypothalamus or anterior pituitary (both located in your brain). Don’t get too overwhelmed hearing that. Just relax. This is all potential talk. If the LH and FSH levels are normal but you have high prolactin levels, this could be the cause of your menstrual cycle abnormality and it may be due to an adenoma in the brain that is secreting prolactin in excess. This excess prolactin may be messing up with the sex hormones. Again, stay calm. Nothing is being diagnosed here. You would need to get the actual work up to get the actual diagnosis. There are a variety of causes of amenorrhea. You are learning some causes and when you go to your doctors you will have a better understanding of what high FSH and LH levels could mean. Or high prolactin levels. Let’s just discuss this without stressing. If your FSH and LH levels are high, then this could mean the ovaries are not being stimulated by the FSH and LH, which may be due to the ovaries not properly working.

History of dilation and curettage from a previous pregnancy and now you are not having regular menstrual cycles?
Then there could be a chance it is due to scarring of the uterine cavity, called Asherman syndrome. This is the most frequent anatomic cause of secondary cause of the absence of menses. If you had a history where you had D&C to remove retained pregnancy due to pregnancy, this has a risk of developing scarring of the endometrium. This then could lead to abnormal menses.

So what next?
You need to make an appointment with your doctor. Your doctor will ask you a variety of questions to establish where the problem could be. Then they will decide what steps to take, which is most likely taking some blood after initially checking for pregnancy with a urine test. Even if you say you are not sexually active, it is mandatory to rule out pregnancy. It isn’t because they don’t trust you, it is because it is protocol. They may do a progesterone test to see why you have an absence of menses and go from there.

I hope this gives you some understanding of what may be going on. Please, leave a comment below if you have any questions and I will be sure to answer it the best I can. My intention is to only teach and not make a diagnosis. You need to see your doctor for the appropriate diagnosis and next step in management.