Fever, cough and cold. Again and again?

My 3 years daughter got fever on 18-feb and consult pediatric doctor he written tests like CBC, ESR,IGE and poriten test. There everything is normal except ESR=36. He told there is infection in blood and given one Anti-botic syrup, cough(s-mucolite) and cold (L -montus kid tab) medicine for 5 days. After 5 days one late night she had heavy coughing and again consult same Doctor again changed medicine only antibiotic syrup. And after two days again she has heavy fever (103.5) on 25-feb after given a bath (lite warm water) and after that consult the. Same Doctor once again he has changed Anti-botic medicine again and done chest X-ray in that rediaology doctor mention that "FEW BRONCHITIS HAS CHANGED " and all other are normal. And my doctor said use this changed Anti-botic for 2 days on 27-feb. But today (1-Mar) she has got little bit fever of 100 f and given colpal-250. But one good thing is from 2 days she is not coughing heavy. May i know the reason why this Fever again and again ?