My period was normal for the first 2 years it came every 21 days for 5 days. for the last year my period has been coming randomly, why?

May be converting: Some people are variable and not predictable. If you were taking the pill initially and not now that could be the reason. Also the body does change at time from regular to irregular. The every 21 days is a little on the frequent side as others have a longer time in between periods See the gyn to make sure all is well hormonally. If so I would not worry.