What Causes Delayed Periods With Spotting And Clots?

26yrs and had my last period on 31/5/2010. from ist week of july this month till date i noticed a brownish spotting, at first i thought it be my period coming or implantantion bleeding but it persisted and started coming out with some clots especially when i clean up.please help even though i'm not feeling any pain.i will appericiate if you reply in detail as i'm very scared,thank you.