What Causes Prolonged Menstrual Periods After Undergoing Exploratory Laparotomy?

Dear Dr, I am 27 years old. I am suffering from endometriosis. I recently underwent exploratory laprotomy due to severe pain in lower abdomen and high fever. The byopsy rrevealed endometriosis cysts. Now the doctor has prescribed me an injection Depot luepride 3.75mg to be taken in 3 dozes every month. I have already taken the first doze on 1st of August 2014. And the next doze is sheduled on 1st of September 2014. But I got my periods on 14 th of August 2014 and it has not stoped till totoday. my last period was on 26th of August 2014 which lasted till 31st of July 2014. Is it normal. ? Or I should not get periods at all during these 3 months. Kindly guide me.