miscarriage? WARNING GRAPHIC!

Hi, I just started my period two days ago and today I felt this gush of blood and I came the the bathroom to find this. I know it could just be my uterus lining but it's much much thicker and bigger in mass than it usually is. (To put in perspective, this is a maxi pad.) For extra information... I am sexually active and my partner and I have had times where we don't use a condom but he has never ejaculated inside me or near me.