Warning involves a question about miscarriage

Just a quick question rather not go into detail but how do you know if you’ve had a miscarriage if you didn’t know you was pregnant? I know this might be a stupid question but just a bit worried how my period has been this month. As I wasn’t due on, I’m on the pill, I was on Thursday to Thursday, off from Friday Saturday and Sunday and came back on on Monday but since the Thursdays I’ve came on it’s been the most painful period I’ve had in my life. But it’s just probs me being paranoid. I’ve made a doctors appointment for tomorrow but just looking for advice really.