Hi there,
if everything checks out by a physical exam, you might want to see an endocrinologist cause it might be hormonal. I had really irregular periods for years too, usually skiiping 2-4 months. I even went a year and a half without one when I was 22 years old. I went to lots and lots of drs and they usually told me everything was fine. I was put on brith control, and only had problems with that, from lots of breakthrough bleeding to still skipping periods.
Then when I tried to get pregnant it took a long time. And by age 30, I finally went into menopause, complete with hot flashes, insomnia, inability to concentrate, waking with fingers tingling, etc. I finally had an ob-gyn figure out what was wrong. I had a pituitary tumor that was producing the hormone prolactin. Prolactin is a pregnancy hormone that is responsible for milk production and elevated levels can cause irregular periods, no periods, infertility, recurring pregnancy loss, galactorrhea (milky breast discharge), hirsutism (male like hair growth), obesity, diabetes, heart ischemia, osteoporosis, and possibly breast cancer. It can also cause a lot of emotional disorders from pms, to anxiety, depression and uncontrolled anger. I'm now taking a drug called dostinex that shrinks the tumor and lowers the hormone level, and i'm having regular periods evey 28 days.
So, the pituitary gland produces 9 different hormones, prolactin is only one, but it also produces fsh, lh, growth hormone, and acth, and tumors can also produce these hormones and throw a womans periods off. Usually, the tumors are not serious and can be treated. An endocrinologist can identify if there is a problem there that needs treatment. There are also other hormonal disorders, like hypothyroidism, that can cause irregular or no periods. I would definitely check out an endocrinologist! Good luck!