I had my menstrual cycle back to back within four days of each other, wht could be the problem?

Several poss. : It sounds like you had one episode of an unscheduled bleed. I assume that you generally have a regular monthly flow and the only real irregularity is the bleeding you experienced after a regular period. After being sure that you aren't pregnant or missed several birth control pills, you could just observe for now and only seek care if this proves to be a persistent pattern. Could check thyroid.