My baby boy keeps getting sick!

Meagon

My 8 month old (born 27+6) keeps getting colds and the flu and now he's in the hospital for pneumonia and bronchitis. I work full time and so he goes to daycare, I take postnatals and I give him a daily probiotic and he gets both formula and breastmilk. Being a stay at home mom is not an option since my husband doesn't make enough on his own to support all of us. Any suggestions for helping him boost his immune system so he doesn't get sick so often?