Period for almost 20 days

Hey ladies, im 17 and i always have regular periods which go for around 6 days 
Anyways this time i got my period on the 25th march, and i thought it had finished the 31st! Anyways on the 1st april i looked in my underwear and i had a little bit of blood, and ever since that day i have been bleeding very lightly and it has been happening for almost 20 days now, has anyone had this happen to them or know why it could be happening?