I can't ever remember what day it is?

I used to be able to remember what day I was on, but I can't seem to do so anymore without looking at the calendar. I can't tell the difference between Saturday and Wednesday; Tuesday or Friday. It's embarrassing when people ask me about the date or my plans and I have to ask them what today is. This isn't something that happens every once in a while. It's every morning, daytime, evening, whenever. On top of that I have to keep my watch strapped to my arm all the time because I have no sense of time at all. What is causing this? I eat properly, exercise, and sleep. What else could it be?