What Causes Body Pain, Feverish And Shivering?

i had cough and sore throat so the doctors gave me amoxicillin and i felt better but the cough didnt go ,i rejoined my work and then i got fever,cough and nose started flowing and then i was said i have got flu so to take rest, i did take rest and now i am back on antibiotocs since the cough has not gone its seem have got chest infection.yesterday night i felt feverish,bodyache and shivering , i wonder why i felt that because in past i had such symptons just for a day and it would disappear the next day.pls help me to understand my case