What Causes Brown Vaginal Discharge With Lower Abdominal Pain?

Hi,

I am 27 years old,, married female. From past 4 days a brown discharge is coming out of my Vagina.Today I think my periods have started but I dont feel any pain in my abdomen or any symptom which I usually used to have during my periods.I have lots of pain in my lower abdomen during my periods which I am not having this time.I had my periods on the 25th of last month(25th Apr 2011). I am not sure if i am having periods only or not. Why was that
brown discharge was coming out before.Please advise