How long does implantation take?

Ilish • Engaged 💍 Expecting Baby #1 👶🏼

The last time we did it (while I was ovulating) was a week ago.. and according to this online calculator I found implantation would be happening right now. I've had really bad cramps/period symptoms/nausea but no spotting yet.. is it all in my head or could it really be happening?