Help Me Practice Japanese By Reading Hentai

I'm going to be completely honest: 60% of the reason I'm learning Japanese is to translate hentai. In fact, one of the many ways I practice my skills is by attempting to read untranslated ero-manga. I'm currently in my second semester of taking college Japanese classes, and while I have a fairly good foothold on the basics, I have quite a long way to go.

Anyways, straight to the point: the sentence structure in the dialogue bubble to the bottom left of this image confuses me. I can understand the words separately, but together it seems a bit odd. I want to say it translates to, "You're not doing my normal self", or something along those lines, but I feel like that's incorrect; the こと right after する throws me off quite a bit. Could someone more proficient in the language help me understand this sentence?