Bad immune system

Has anyone ever had an awful immune system? I mean I get flu like symptoms and a fever every two weeks (maybe a little exaggeration but it's really really often)... It usually lasts 4-7 days and then I'm fine. My immune system is pathetic. Has anyone ever had this problem? Does anyone have tips? I'm in shape, drink plenty of water. I take vitamin b12 and iron due to deficiency in both.. What is wrong with me? I hate being sick. I'm such a baby and I want to cry.