Symbicort (budesonide formoterol)

My son has frequent cough and colds ever since he was 3 years old. He was diagnosed with primary complex last year (2007) and was treated for 6 months. After the medication his doing well but then it started to come back again. As his pediatrician told us that he has Asthma and was advised to take up "symbicort" and "montelukast" as his daily medication. She will only advised us to stop the "symbicort" until such time my son gets well. Isn't it  too much intake of "symbicort" wont be having any side effects to a 5 yr. old kid? I heard that this medicine has steroids right? So, is it not harmfull to him? Does it affect his weight as well his behavior? My son right now is loosing his appettite and getting worst. So his doctor told us to continue the medication.I'm just concerned that my son at a very young age his body is already full of antibiotics. I need your advise for this.