What Causes Blood Clots In Menstrual Flow With Stomach Pain?

me and my partner have been trying for a baby for about a year, on the saturday just gone i started my period, but was having very bad stomach pains, for the whole of saturday i was clotting and had quite a big 1 at some point, i checked online and the symptoms i had suggests i miscarried, is that rigfht or is there another explanation, if so what should i do ?