What Causes An Outbreak Of Itchy Red Blotches On The Face And Arms?

I am a 23 year old white male, and partially overweight. I have been at school and work for 3 days since the start of the quarter and am doing 14-15 hour days on my feet and walking around. This is walking from class to class and then working at a retail store as a cashier. I m just getting over a soar throat with a cough. Ive been using my normal clothes and same shampoo and soaps etc. At around 5pm (now being awake and moving for 10 hours doing my routine schedule) i started feeling heat on my legs it progressively got hotter on the extremeties of my body, including my face, ears, arms and legs. They are red blotches. Some of them are itchy and irritated but not all of them.