Get some graph paper and make a
chart. Write 1 - 32 or 33 across the top (turn the paper sideways). Those are your headings. Every time your period comes, begin a new line under it. Under the 1, write the calendar date when your period begins. Use red ink for the dates of the days of your period and black ink for the dates of the other days of your month, putting the second day's calendar date under the 2, and the third day's date under the 3, etc.
1 2 3 4 5 etc.