What Causes Constant High Fever, Stomachache, Vomiting, Diarhhoea And Pneumonia In Children?

My daughter is 4 years old and since she was very young, she has had issues with high fever, stomache aches and vomitting, diarhea, and brochitis/pneumonia. We have been told countless times that it is due to daycare and she will grow out of this constant illness, but she hasn t been in daycare since May and is still very sick. (We go to the doctor almost once a month). I heard of something on the radio about children who are always sick with the same constant problems and how to identify and fix the problem and was wondering if there was any truth to this or do you suggest having another doctor or specialist look at her?