Changing cycle?

My cycles have been 6 days (five bleeding, one spotting), on a 36 day cycle, my whole life.

Suddenly, after my last birthday (22 in December) it changed to 3 days (two bleeding, one spotting) on a 28-32 day cycle with cramping that is way worse.

This has been consistent every month since.

Is there a reason for the change, or is it just normal hormonal changes?