Negative, right? :( AF 3 days late!

Brooke
Whyyyyy do I keep getting negative tests when my period is 3-5 days late based on my 25 day average cycle. It's now at day 31 and still no period! I've NEVER been late before more than a day. My period is usually very irregular but I always get it early or on time 23-27 days. 
No hope? Maybe I'll try a first response test since this is from eBay? If my period doesn't come soon there must be something off
Tweak anyone? Thank you!