What Causes Irregular And Prolonged Periods After Giving Birth?

hi i had a child 3 years ago.for the first year or so after the baby i had my period.not like a normal peroid but spotting,one day i would bleed and the next i wouldnt.when i went for the injection,the nurse advised me that i couldnt get it due to the fact that i was bleeding for so long and that i should see a doctor.i thought it was nothing and went to a different clinic where i didnt tell the nurse my problem,and i got the injection.the bleeding then stopped until i forgot to go for my injection a month or so ago,i got my period which lasted almost 2 weeks then i spotted and i started bleeding heavily last night.its dark dark red,like almost black or brown in colour.and since i gave birth i have been feeling ill on and off,weak,light headed(like the flu symtoms) no evergy...please explain