implantation bleeding or Ovulation bleeding or periods?

So, I always had regular periods but since last two times I used to be 4-5 days late from my supposed time. So in Oct 6th I got my periods, My doctor prescribed me lezra tablet for 5 days and ivf m 150iu injection on third day. I baby danced twice or may be thrice I am not sure after my periods ended. I have no Idea when was my ovulation. So on 19-20th October my nipples became really very hard amd started to hurt. and they are still hurting. and on 22nd Oct we baby danced again and found out dark brown discharge. Since, yesterday I am getting dark brown very very light discharge. I didn't get any cramps but I feel tired and lethargic. So today is my 18th day of my cycle and I have no idea if it's early periods, ovulation or implantation bleeding. anyone had the same experience? please help