Implantation VS Withdrawal

I've recently stopped taking my birth control and two days after I stopped I had unprotected sex with my boyfriend. My period was already 9 days late when all of this took place. Now I am experiencing some very light dark brown/bright red blood. It's not my period though because my period has a very distinct look and smell no matter how light or heavy it is. I'm not sure if this is withdrawal bleeding or implantation bleeding I'm experiencing. I only stopped because I'm switching birth controls and my doctor advised me to do so.