Spotting

Okay, so I had sex with my ex boyfriend 2 weeks ago (stupid idea yes I know) and ever since like 4 days ago I have started spotting, but I finished my period 3 days before I had sex, does anyone know what it is? It goes from like brown blood to bright red blood. And I don't know weather it is something to be worried about to go to the doctors :/ anyone help me out.