AF 3 days Late!

Kait

My fiancé & I have been TTC since April 2017. I’ve tracked my period each month since then and never have I been late, each month is spot on. I was due for af 1/12/18 and now three days later I still haven’t gotten it, I tested earlier and got a BFN😭😩 Should I wait a few more days and retest or do you think af is just late? I’m not stressed or anything so I’m not sure why it would be late, ugh!