BFN after possible IB

Em
Im now on CD24 (the day I would usually get my period) and from CD17-19 I had what I thought was implantation bleeding but tested this morning and got a negative... having all the same symptoms as my first pregnancy and also had implantation bleeding with that pregnancy and had a negative test before a positive last time... I'm 5 days after the last day of spotting I would have thought it would be positive if I was pregnant. Thoughts?