What Causes Vaginal Bleeding While On Marvelon?

I have endometriosis and am anemic and my doctor has recommended I take Marvelon continuously to reduce amount of bleeding and loss of blood which has lead to my anemia (as my periods are very heavy,usually 7-8 days long). I am now at day 56 of continuously taking Marvelon and have had spotting last few days, which is becoming heavier today. Should I give myself a period by now going off for 7 days?