I had unprotected sex for 2 years 2-6 times a month, usually right after my period ended or right before it started, never got pregnant, is it normal?

Old rhythm method: This is a variant of the old Catholic rhythm method of "contraception". Better to be "lucky" then "good" as there are many Catholics in the world who are here on the planet when this method failed. Although those time periods are "low risk" for pregnancy, that does not mean no risk..

Ovulation: In a female an egg is released from the ovary into the fallopian tube (ovulation), where during a 24 hour time period it can be fertilized, if sperm is present. Ovulation occurs cycle length minus 14 days. A cycle is counting from the first day of the menstrual period to the day before the next menses. In a 28 day cycle, ovulation is on day 14, in a 30 day cycle on day 16 a.s.o.