I am 43. I usually have very light periods that are either a few days late or a few days early. Yesterday, I got my period at 8 days early. It started brown then proceeded to be extremely heavy with large clots with heavy cramping. I bled all over myself unexpectedly, which has never happened. I used a tampon every 15 to 20 minutes for about 8 hours then it tappeded down to about one an hour. This is still the pattern. I had a tubal at age 28. Is it possible I got pregnant and am having a miscarrage?

Yes, that is one possibility. The best thing for you to do is to see your doctor ASAP (as soon as possible)