Implantation or late period?

My boyfriend and I had sex this past month and he accidentally came inside of me. I was supposed to start my period on the 22nd but I’ve been having cramps since that day, the same kind of cramps I would have if I were on my period, but there is no blood at all. My period has been late before but I’ve never experienced cramps on the day it was supposed to start without actually having a period.