Period or implantation?

I had unprotected sex jan 24 although he did not come in me, and I don’t believe I was fertile. I took a plan b about a month ago so it messed my previous period up and made it short and came on sooner so I’m irregular now. I just wiped and it was a little pink and I’ve had no discharge today at all, is this my period starting probably or could I be pregnant and have implantation bleeding? I’ve had pain in my lower left back all day and starting to feel light lower cramps.