Hi, I Experienced Some Discharge The Past Cpl Days Along

Hi, I experienced some discharge the past cpl days along with a tissue like substance. I started my period today, but the blood is very dark brown and thick and I've seen a cpl blood clots in toilet and I'm saturating my tampons rather quickly and bleeding thru to my under ware. Should I be concerned about a miscarriage? As far as I know, I wasn't pregnant but I'm sexually active with boyfriend who is fixed but I know some ppl have gotten pregnant still when husband/ boyfriend is fixed. Thank you for your time.