What it means to have to have two periods in one month why is that?

Normal periods: The normal menstrual cycle is between 21 - 34 days. Therefore if the last menstrual period is during the 1st part of the month, then it would be normal to expect a second period toward the end of the month. This is normal. Always count from the beginning of the 1st period to the beginning of the next period. If the number of days is between 21 and 34 then you are normal .