What should I do?

May

So I’m new to periods, (just got my first 4 months ago) and my period ended 2 days ago. I had no bleeding at all yesterday or the day before, not even spotting, I had a heavy flow like normal and it just got medium and then stopped.

I was on a walk this morning with my dad and I felt and stabbing pain below my belly button and it escalated to me not being able to walk and I am still in a lot of pain. I made it home, went to the bathroom and there was a lot of blood. My whole pants were soaked through.

I don’t have a fever, there’s no chance I can be pregnant, and I am 13 years old. Can this be a serious problem or is this normal? I am freaking out, please help.