Falling sick every month

Hi mummies, does your LO tends to fall sick every mth? Mine falls sick every mth ever since he started attending IFC... usually it is always the runny nose and cough (resulted in sensitive airways). Is it normal to fall sick every mth at Toddlers' class? LO is 21mth now. Brought him to two PDs and both said is normal. Then again I dont feel good when LO had to consume antibiotics and those flu medications every month. Probiotics, airtumtec are given everyday. Helps.