Painful cramping after unprotected sex

Hi! So my period ended Friday and my bf and I had unprotected sex on Saturday. We don't do it often, but we did but I am on birth control. (But not taking pills currenty because I was on the week of my period). Usually I experience a little cramping but I cramped all day (badly) and I spotted more than usual. Sometimes I spot which is normal because my period is short( wed-Fri Morning ish). Is this a sign of implantation or am I nuts? :) I resumed my birth control today and there isn't any spotting, just small cramps. Thanks!:)