There's nothing to be sorry about. It's natural; women menstruate. Get an over the counter pregnancy test to rule that out first and go from there.
A gynecologist can find out for you. If it's for 6 months and the belly isn't as big as a melon then you better seek medical help and not some online strangers. Either the cycle isn't starting for some reason like hormones or something is preventing the uterus from creating\ shedding the mucosa lining.
Everyone has already said my advice but I'll repeat.
1) Call/Contact a Professional / Doctor and probably set up an appointment.
3) Premature Menopause
4) Something's not behaving normally.
Like everyone else on here said, no one better than a gynaecologist. When you said less than 40 years, I assumed an age >35. Limited as my knowledge is, I think I can safely state the following possibilities:
-Pregnancy and lactation.You can rule that out yourself. (Urine hCG, USG)
Could it be menopause? Clinically, this could be two ways, one is that your periods were normal and suddenly stopped for 6 months with the clinical features of menopause(hot flushes, sweating, insomnia, etc.) or this happened with a gradual increase in the spacing of your periods(a Climacteric), Well, either way, Premature Menopause is suspected when it occurs before 40 years. By definition, menopause requires cessation of periods for a year, But if you had no periods for at least 3 months, your doctor may advise an FSH and estrogen and that will confirm a premature menopause.
There are many other causes, that would be ruled out by your doctor in the history:Are there any other symptoms? Any abdominal pain, discharge pv, any of the v.s menopausal symptoms, any abnormal weight gain or weight loss, undue fatigue, etc? Before 6 months, were your periods normal? Any surgeries, procedures in the recent past? Recent traumatic childbirth? Any other comorbid conditions? Any medications you’re on? A hormone profile would rule out other medical causes.
To cut this short, there’s more than a sentence your doctor will require from you, and on the basis of the story your history tells +/- some tests, the doctor will counsel you any further.
See a doctor and it’ll save you lots of unwanted thinking and unnecessary googling.
I wish you lots of good health and happiness.
The best advice would be to see a doctor. There’s nothing to be sorry about. Periods are physiological and we all have problems with our bodies sometimes. Now go get an appointment.