How Can Irregular And Light Bleeding Periods Be Treated?

hi im 20 years old and i usual experience 7 day long periods with heavy bleeding and menstral pain. for the past year and a half i have been unsucessfully been trying to get pregnant. now i am tracking my period and for the past three months my periods start a week earlier than usual and are very light one pad a day with no cramps. my supposed period ended may 1st. may 10th i had sex and the next day i bleed for 12 days. why is this happening?