What Causes Excessive Bleeding During Menstruation?

i dont have menstruation for about 1 1/2 month.This july 2014 i have menstruation for 1week but my spotting continue up to 10 days. I went to my OB then she advice me to have an ultrasound. I am not pregnant. The finding was normal size anteverted uterus slightly thickened intact endometrium polycystic ovaries, bilateral. Then my doctor gave me a pills named althea to stop the bleeding. I took it during that night, the day after the bleeding stopped. But then after 1 week the bleeding came back excessively. I consulted again to my OB she gave me hemanex 2capsules 2 times a day but after taking that medecine it continuous again the bleeding. Please help me