しまくる as a form of する?


I'm reading a book, in which a character is confused.

They use the phrase 混乱しまくる (こんらんしまくる)

I can't find anything with しまくる on any dictionary sites and googling the
grammar for it comes up with nothing helpful that I could find. I think it
might be a form of する but I've never seen it before, so I have no idea what I
means

