Irregular menstruation is very common these days and is often due to some form of hormonal imbalance. Do you know what type of blood work your doctor ordered for you? It sounds like you have periods amenorrhea. An absence of menstruation for 3 or more months in a woman who has previously menstruated is called amenorrhea.
The most common causes of amenorrhea are:
PCOS or poly cystic ovarian syndrome
Abnormal prolactin production
Hypothalamic related causes
It sounds like you may need to find another physician who is willing to work with you to find out what is causing your irregular cycles. It is great that you are trying to figure this out now and not in 10 years when you are desperate to get pregnant. I would recommend finding a qualified Naturopathic Doctor in your area to work with you. www.naturopathic.org is a good place to start.