My 2 year old boy has frequent ear infection, chronic sinusitis, asthma, frequents diarrhea, and loss of appetite. . Since he was 6 months he is always sick. Periferal smear show slight poikilocytosis and burr cell. RBC- 4,25, Hgb- 12.3, HCT- 34.5. He also has history of vitamin D deficiency (26.10). What can cause that he is always sick? What other testing he will need?