Hi. i constantly feel sick and rundown. i sleep enough each night but everyday there's a different illness. one day i feel fine and the next day i feel tired and exhausted. it feels like it affects my performance at work. what can it be?

Be time to see Dr.: Normal, healthy people do not have "constant tiredness," without a good reason. One's primary care doctor can follow along and look for reasons for fatigue, such as anemia, infection, mental illness, auto-immune disease, thyroid problems, cancer, insomnia, etc... Various tests may be needed, depending on one's whole story, and sequence of symptoms.