Help!!!

Alex
So my "af" came on time, EXCEPT ever since the 12th (the day I was due to start) I've been spotting and ONLY spotting and only had mild cramps one time on that first day. 
Normally my periods don't last longer than 4 days, and it's now been 7. 
Still spotting. 
Pretty sure I got a faint line on a blue dye test but I could just have line eyes. 
Any ideas??