What Causes A Thick Discharge Instead Of Menstruation?

i am 16 and i frequently get irregular bron sticky thick smelly liquid discgarge. i had an ultra scan 7 months ago and it came up with 2 cysts in my ovaries and a month ago i had another one and it came out clear. but today i should be expecting my period and insead a thick stick dark brown liquid is coming. what isit? is it bad for my health?