Period restarting ?

I started my period on the 11th of this month. And I recently been using menstrual cups for about 3 months now, my period is usually about 7 days the last two days are always pretty light and barely anything comes out but I still count those days. But strangely yesterday (15th) I really didn’t have a lot of blood and that’s usually normal so I took out my cup and just put on a panty liner and a couple hours later I just started cramping and bleeding bright red blood again. Why is that? I’m never experienced this before. And I usually don’t cramp this far off into my period.