Why am I spotting?

I am 9 DPO I had sex in my fertile window a few times , I wasn't trying to conceive just letting things go with the flow but I'm due my period in 5 days but started spotting today and yesterday, I'm am very regular with my periods and always have been , it's very light bleeding and pinkish colour, I took a pregnancy test today and had a BFN , I know it's probably to early to test but does anyone know could that be a sign of pregnancy or implantation or am I just getting a period early?