Have you tried taking a daily supplement like Emergen-C? They are little powder packs you dump in a glass of water. I just take regular Vitamin C, but my boyfriend swears by the Emergen-C. Be sure to drink lots of water and eat healthy. Seems like such a small thing, but it can really help keep your immune system up. And try to get enough sleep. My biggest problem is the sleep thing. I always sleep horribly the first night away and if I am in a different place each night, I am wiped by the end of the week. Also, make sure you wash your hands a lot. Carry hand sanitizer and wipes with you everywhere. For flights, I wipe down the tray table before I put anything on it. Oh, and maybe talk to your doctor. Mine added B12 to my daily regimen. Good luck!