My Period Has Lasted Three And A Half Months, And

My period has lasted three and a half months, and I went to a doctor about two months ago to see what the problem was. she tested me for anemia and I was negative. Recently, about four weeks ago, I went to a gynecologist and she gave me birth control to regulate it. now, I've been feeling light headed and my head throbs when I walk/stand up. what could be wrong with me, and what do I need to do?