Welcome to HCM.
Since you have got a complete medical checkup by an E.N.T. surgeon and he is of the opinion that there is nothing serious to worry about, I think you can rest assured that there is nothing wrong with your child. Running nose and common cold
do cause breathing difficulty, i addition to deviated nasal septum
Best is not to over treat the condition as it may do more harm than good. Our anxiety
for the health of our child could also lead to over caring and getting worried for minor ailments.
Wishing your child all the best.