Hi, I Thought I Was Pregnant, I Was Three Days

Hi, I thought I was pregnant, I was three days late, and then I had spotting one day, nothing the next and then the next night I woke to intense cramps and was heavily bleeding. I had a golf ball size clot come out and then a bunch of smaller ones for the next to days. I have now stopped bleeding for two days but still feel pregnant. My question is, can implantation bleeding be very heavy and painful, more so than a regular period or could I have had a miscarriage?