Late period why ?

Es

Soo last Saturday me and boyfriend had sex at 10pm he cummed inside of me and the next morning I went to Walmart and bought the plan b within the time frame . I bought it that Sunday tho ! And I was suppose to start my period that Sunday according to <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> . And <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">eve</a> always is accurate and my chance of pregnancy was at 3% . And soo here I am 3 days late wondering why 🤕 help me out is it because of the plan b or pregnancy.

Update soo I went and took a pregnancy test it came back negative. When I was day 3 of being late . And now I’m on the 10th day of being late . Is it possible that I took the pregnancy test to early and I should take another one ? Or is it just a waiting game for my period