Miscarriage???

So I started what I believe is to be my cycle. Usually has been coming on time every month. This time is very weird. About a week before I started I was very nauseous some lite vomiting and a lot of back pain. Today I soaked 2 kotex pretty quickly and had about 3 clots one being very big in size and the others pretty decent size. I've had clots before but it has been a while and they were never that big. I did a pregnancy test before and was negative. But now I'm really sick to my stomach and had some really bad cramping almost like contractions. Is this a miscarriage?