Another period!!

Hey ladies, my period came late in December. Usually, I have my period in the beginning of the month but for some odd reason, my period came December 27th to the 31st and here I am January 12th & my period came on January 11th. I have been sexually active with my fiancé. But I don’t understand why my period came again instead of at the end of this month. Any advice? It feels like i just had my period not too long ago. I havent been under any stress