A little worried about my period?

ok so im 20 and i got my period march 3rd and i usually have it for about a week but i was done it on the 10th and now its the 13th and im startin it again is this normal to have it twice in on month its never happened to me before i got my period when i was 11 and for a while id get it once a month sometimes id have it for one month and then i would go for 6 months without gettin it up untill about december when i was gettin it on time like i was spose to and now im haveing it twice in one month is this normal has this ever happened to anybody before