I am on yasmin, and i have been for atleast a few years.?

i cant remember exactly how long. i have notice within the past 4 months, that if i miss a day and forget to take it, i will start my heavy period that does not ever really stop. i have break through bleeding almost weekly. this has been going on for about 1 - 2 maybe months. it is really started to freak me out... i dont know what to do. i made an appointment to get checked out. any ideas or info would be amazing. thank you