I think some kids do go through the stage when they always get sick.
Mine was never sick until he went to nursery. He was admitted twice in hospital. One for RSV and one for severe asthma. He was 2 and a half by then and I was very worried too.
Thankfully he seems to be growing out of it and his asthma has not come back for almost a year now. But of course he is still on daily Pulmicot.