Is this a miscarriage? Or normal after a late period?

I have been trying to get pregnant, however, not been successful, at least I dont think I have... I have had my period, but have been late. Last month I was about 3 days late, nothing to be worried about. Then this past month, I really thought I was pregnant, but my period came and was about 10 days late. I had a normal period for about 5 days (which is the norm for me for I usually have my period for about 4-5 days) then I thought it had stopped. Then 2 days later I spotted a little that was brown and then pink. On the 3rd day, which is today, I got up out of bed and felt something so I went to the bathroom and there was huge clots of blood. (sorry to be so graphic) I have had some minor clottiing before, but NEVER this much. What can this be from? I am 34 years old and my periods have pretty much been regular until the past 2 months, which I have been under alot of stress, so I wasnt too concerned about the late periods until I passed these clots today. Is this normal after a late period? Or could I have had a miscarriage?