2 days late. Negative test. HELP!

I had unprotected sex July 4th, one of my fertility days. I've been having symptoms, I know what they feel like since I already have a son. ♡ the first two days after I d sex, I had extremely spre breats but it disappeared. I had a little bit of nausea and some heartburn. I took a clearblue digital week estimator the 18th but it was negative. I was supposed to get my period yesterday but she hasn't showed. Has anyone ever gotten a false negative on one of those tests?