Ah ok that makes more sense. Is there any discolouration or indication of excess heat on the phone or its buttons? If not, it could potentially be a case of a cheap case with low heat tolerance.

If you want to be sure, you could always try contacting Apple Support to run tests. It’s possible the battery could have issues. That’s the most likely thing that could cause an inordinate amount of heat.

I’ve never seen a bulge in that spot before. Is the screen still flat if you look at it from the side or is it protruding out?