Fast breathing. Sudden high fever now?!

Hello doctor's, my child is 2years one month old, weighs 12.5kg, he's been having cough and vomit from Monday night and elevated temperature of 99.5, we consulted our pediatrician and was given asthalin and monticope, from yesterday he's been having this noise breathing, and severe cough, I did went to ER last night, and chest xray was done becoz of mild trachea , doctor said he's perfect and nothing is wrong in his xray.., again today evening he had a temperature of 101.9, we have given him sponging and fever reduced. Medicine given now is lanzo junior, asthalin, Amoxicillin, and emeset as sos, the ER doctor did say that he has a bad nose block, hence trachea and fast breathing. Breathing per minute is 28 to 31, when he's sleeping. Oxygen level was 98 when we checked last night at the hospital. My question is why this sudden high fever now?! His chest xray is clear then what's bothering my child, please give me your suggestions doctor's, thank you