I didn't start my period till I was 16 and would have them very infrequently. At first we thought it was because I was so active in sports, but continued to go for months without having a period after I stopped being so active. I had my first child at age 19. Once I had her I went on the pill which made my cycle "normal". 5 years later I went off the pill in an effort to have another child. When I got off the pill, I didn't have a period. My ob/gyn said that you need to have a period every 8 to 10 weeks so every 8 to 10 weeks I would test my self to see if I was pregnant. If I wasn't pregnant, they would give me a drug that would cause a period. After the birth of my second child, I went back on the pill and of course was regular again. A year later I went off the pill and after a few of the 8 to 10 week drug treatments to cause a period, my cycle began to start on its own. My cycle is now on 40 days instead of what is normal at 28. My doctor says there is nothing abnormal about not having a period regularly so long as you do every 8 ot 10 weeks either naturally or drug induced to allow yourself to be "cleaned" out. Hope this helps.