Are the clearblue digis (w/smart countdown) accurate?!...I'm soo confused!

I'm 14 dpo & afs due today...i took a test and it was negative...i have NO symptoms of af showing her ugly face at all! Have a slight backache, pooing more, sometimes diarrhea...TMI i know...And my uterus is feeling tender...what the hells going on?!...anyone else test with these and get a neg past 14dpo?!...I've heard some bad reviews...but I'm probably just hoping too hard! :'(