Please Help. Is it implantation bleeding?

Hi everyone, My af was on 1st April and I BD thrice during the fertile window (as per my trackimg app). Now on CD 20 and 21 i have had spotting. It started with light pink on CD20 and became dark brown on CD21. My cycles length is approx 26-30 which means I am not due for another week. Please help. PS: Sorry for TMI.