Unsure if miscarriage or early period

Hello ladies, so I've been on the pill for 6-7 months and have been taking it on time ever day but I started spotting and then bleeding early. I have had intense cramping in my stomach and lower back for 3 days now and I have noticed a fairly decent sized clot tonight. My period has never been early while on the pill and my cramps have stopped since before the pill. Any ideas what could be going on??