I am 23 i had my period 13 days ago?

i am 23 i had my period 13 days ago and was unusually painfull and heavy. i have now came on again. My periods are usually very reualr and on correct times. I am in a ual relationship and have been for 6 years and have not got a std. I am takin the mini pill(femulux) which i take reagrds to weather i am on my period or not.