Possible miscarriage

I had one Positive test about 3 1/2 weeks ago left it a few days and have been negative but having symptoms and real bad heartburn with pain. I called the doctors last week and had blood done. My HCG levels came back as being negative but I have now started what I think is my period possibly miscarriage. I it is worse than a usual period I would normally have, plus small clots size less than 5p which I normally don’t have either. so I don’t know if it is impossible miscarriage or just a bad period. Anyone had this and just been a period or has it been a miscarriage?