Could it be implantation

I'm on seasonal birth control which means I only get my period four times a year, my next period is due late September. Two weeks ago my fiancé and I haI unprotected sex(other than the pill) amd he did not end up pulling out before he finished. Yesterday I got really crampy and when I went to use the loo I noticed a smear of browninsh black blood, not a ton, but it was noticeable. Today again it was there as were the cramps. Is it likely that that is implantation bleeding? Or am I over thinking things... I've been on the pill for about a year now so my body has adjusted to the changes.. Please get back to me!!