help? TMI!!

I came off the pill at the end of June and haven't had a period. today I've woken up soaked in blood, I started spotting yesterday so I put a tampon in, I changed it at 6:30am this morning and by 9am I went through my tampon, my pants and my trousers and even my bed. as soon as I took my tampon out it gushed out. I lost this blood clot when I took it out. I've never lost a blood clot this big and it's worrying me. could it be a miscarriage or a really heavy period?