Could it be a miscarriage?

5th day of what I thought was my period... 2nd day I had strong cramps which felt like contractions, never felt anything like it. My back was hurting so bad and also felt a sharp pains on my right butt cheek. I bled through plus tampons like crazy even with a panty liners and onto my clothes. Im on my 5th day of my period, by this day as my normal period it would have slowed down. I still have cramps, I pushed lightly on my belly and it hurts. I usually have heavy periods and but not like this. I really don't want to think anything of it but it's hard not to.. the pain is unforgettable.