Any ideas

So my period is now 20 days late I have never ever been this late. The weekend of Valentine’s Day I had this only when I wiped I thought it was my period but it lasted maybe three days and stopped and never got any heavier than this. My friend says it’s more than likely implantation bleeding anyone else have a theory? I have taken tests but they have been negative so far but I’m concerned because I’ve never been this late after this week I’ll officially not had a period for February and I have a period every month.