He'd designed the armor to be more-or-less comfortable; after his experience in the Mark I armor, he rather insisted on it. But there was only so much to be done when the armor had to protect him and had to fly; he cold make it aerodynamic, and had designed the distribution of weight and the skintight undersuit, but he couldn't make it anything other than inflexible metal plates encasing him and forcing his back into unnatural positions.
For twenty-four hours, he could handle it. Anything after forty-eight got...long. He'd hit seventy-two now, after popping out of it briefly early on to tinker with the heating and filtration system. He wasn't exactly warm - he'd had to break ice forming within tiny gaps between armor plates more than once as he flew through ice storms - but he had warm enough air circling through his helmet and into his lungs.
That still left him flying and fighting in a very stiff and confining suit of armor. The moments he had to himself to think, he could concede that he was tired and sore and battered and wanted something hot and a few hours of sleep before he went back out there. But the part of him that couldn't stop kept finding the next target, and then the next, finding the people who were trapped in their homes or the giant that wasn't already being taken care of, or a section of the power grid that was flickering and failing, or there was someone scamming civilians. How could he stop and rest when that meant people would get hurt?
JARVIS connected Pepper through without inquiring as to whether Tony actually wanted to talk to her, and he batted her image down with uncharacteristic shortness. "Little busy now, Pep," he told her as he banked and headed for the harbor that was rapidly freezing over and cutting off needed lifelines. "Check my schedule for, oh, sometime next week and pencil it in."