(NSFW?) Could I be having a miscarriage?

Firstly, before you get on me for asking on here instead of going to the hospital, if it is happening I won’t be going to the hospital unless the bleeding doesn’t stop in a week or so (I’ve done my research and have known several people who’ve been through countless miscarriages). Secondly, I will be telling my mother what’s going on I just want your opinions on the situation first. So I just finished my period on the 2nd but I started bleeding again lightly on the 6th. I didn’t think much of it, my periods have always been really irregular so I just assumed it was normal for me. But yesterday it got really heavy and I started having really bad crampy feeling things. I’ve gotten menstrual cramps maybe twice in my whole life and never as bad as this so it alarmed me but I still just popped a couple Pamprin and went on with my day. Then I noticed that there were hard-ish clumps in the blood which has never ever happened to me, and there were a lot of them. The Pamprin cut the cramps way down but it happened again today. I didn’t think I was pregnant and I took a test this morning and it showed negative. My breasts and “down there” are really sore. Could I have had/ be having a miscarriage and is there any way to be sure other than going to the doctor’s?