What Causes Prolonged Period And Headache With History Of Ovarian Cysts/endometriosis?

iv been on my period for 18days now, the color changes from bright red todark brown its not real heavy but enough to worry me. iv been feeling tired, getting headachs,cramping off and on and have been feeling sick to my stomach to the point where i actually threw up last night. i have a history of ovarian cysts and mild endometrioses, please help.