Period

Patient: I started my period when I was 11, and it was normal. At 15 it started coming every 2 -3 months and as I get older its farther apart. Im 18 now and i have a period anywhere from every 4-6 months and sometimes even longer in between. At times when I do actually have them half the time they don’t last more then four days. Is this normal or what could cause it?

Doctor: