Confused!

This month I had sex around ovulation and I had spotting, cramping, aversion to sex temporarily and I was extremely fatigued. My period was due on the 26 and I took a pregnancy test on the 27 with a negative result. I don’t understand how my body would come so close to tricking me.

I had nexplanon for several years until Jan of this year and I’ve only menstruated once since then last month for a few days. I’m just confused