What Causes Heavy Periods And Thick Brown Discharge?

hi.ive been having problems with my period since i had my son 18months ago. i was went back on the injection afterwards but started to get heavy periods lasting up2 3weeks then i would get brown/black thick discharge and be back on again.i went to my gp and he refered me to a gyno who did a scan and biopsy all came back ok.i came off the injection and been using condoms.my periods stoped for 4months had heavy red periods sinbe april but all of a sudden i came on my period on 22nd may fin on 30th then on the 5th got that thick brown/black discharge again then came on a period again on the 6th til 11th i went to toilet last night and had thick brown discharge. Can you help if feel like im going mad?