In march I came on my period on the 12 and in April on the 7 now its may and I came on the 11whats going on this never happened be for

It seems as if you are not on a regular period schedule yet. Don't be alarmed! It can take anywhere from 3 months to 3 years to get an expected schedule. Every girl never just starts her period on a perfect monthly day. For now it can come at any given time.