What Causes Fever, Tired Muscles And Hot Sensation In Body When Exercising?

Hello, I have a question. I am a 5 8 22yr old male who has always been relatively healthy. Around December 8 of 2014 I decided to do the sport of Boxing, and the first week of intense training I got really sick, fever tired muscles and hot sensation all over my body. I took time off got better and went back, however not long after I got sick again, same symptoms. Now, having taken a week off I went back feeling fine and here I am feeling extremely hot, exhausted and weak. What gives? I also ate 5g creatine before going?