Is it strange to get your Period/ Menstrual cycle early?

I mean to ask this because I have experienced that every 21 days or less I am seeing my period and sometimes twice in ome month. The last time I saw my period was last month in february towards the end and now it began this week. I dont get it and I checked the calender and it seemed a few days early thsn usual. Do I have a medical problem or should i not be worried about anything?