Implantation bleeding question

So I know very few women get implantation bleeding. I have been having unprotected sex all month and last night I went to the bathroom and saw light pink blood on my underwear. When I wiped nothing was there. Now this morning I am having light pink/brownish spotting. My period is due in 4 days. I dont know if this is my period starting early or implantation bleeding. Has anyone gone through IB before and if so was it like this or was it different?