Has anyone felt implantation?

Earlier this week around the mon and tues, I felt like crap, mild low back pain and mild cramping...but it has disappeared since then. Well I'm suppose to start on sat, really hope I don't. Anyway based on everything I've researched and all the calculations from my last cycle, they said my highest chance of implantation would of been this past mon; one of the days I felt off....anyway, has anyone else been in a similar situation and if so what were your results?