Hi i had a normal period this month came of for 3 days in those 3 days i had sex and today i have another period starting.. first time this has happen?

Once a year?: A woman with cycles shorter than 29 days (shorter than 1 month) will likely have 1 ovulation per month during the year, but have 2 ovulations during one month of the year (since she has about 13 cycles a year). That means she is likely to have 2 menstrual periods during one of the 12 months of each year, because she has 13 periods a year.