A rise in body temperature is to be expected, it is a lot more exercise than it may seem like. As for sore throat...are you warming up ahead of time and gradually working your way toward the outsides of your range? Just like a runner who doesn't warm up their leg muscles before they run, a singer can experience strain if they don't warm up. Also, are you in an area with high or low humidity? One of my biggest challenges living in Wyoming is keeping enough moisture in the air to be able to sing without straining against the arid climate. Other than that...do you vary the place on the scale that you're singing? If you get up to the outside edge of your range and stay there for a length of time, you will also experience strain from overworking your voice, so don't forget to dip back down into comfortable levels at regular intervals. Hope some of this helps, that's all that comes to mind at the moment :).