What Causes Irregular Periods, Mid Cycle Bleeding, And Bleeding After Intercourse?

i had taken the injection last year 2009 took it once and never took it again after 3mths when it was due. my periods took long to come and also have been irregular. i also find my periods are coming evry other month and lasting for 2wks also after periods im still getting little bleeds like when i go toilet and i wipe there will be alittle bit of blood on the tissue also after sex some times its brown i dont understand why and also when my partner discharges inside me it always comes out with blood does that mean i cant have any kids.