No period in 3 months, and not pregnat.?

I have no idea what is going on, and I have my doctors stumped. I have not had a period in 3 months. I cramp 2 weeks before and 2 weeks after , but still no period. Any help will be much apprecieated.No period in 3 months, and not pregnat.?
Do the doctors think this sort of thing is unusual? It isn't.
My mother lost her periods for months when she started teaching. The doctors back then were pretty barbaric as well as ignorant, and they nearly decided to give her a hysterectomy. Lucky they didn't: she had 5 of us.
Up until my first child I didn't even have a recognisable cycle most of the time. I have 2 children.
Have you had a stressful change of circumstances in your life, positive or negative? More exercise? Slimming diet? Even falling in love can put your cycle out (if so, it comes back when you get to the comfy-together stage). Or are you living with other females, in which case their pheromone cycles can upset yours?
It's right to get it checked out medically, but if they've found nothing wrong, I wouldn't worry.
My condition of amenorrhea (absence of a menstrual cycle) has been tracked back to prolactinemia - I have pituitary adenomas - a small cluster of benign brain tumors - all of this has caused my periods to cease. (Hooray! Who wants a period anyway?! LOL) My blood tests showed high levels of prolactin. I'm taking bromocriptine now to shrink the tumors and restore some sense of normalty. If it doesn't work, and the tumors grow, I will need brain surgery.
weird? have u been sexually active? Or in sports u like lose your period. It happends.