You could have a vitamin d deficiency as that can lead to tiredness and fatigue, but to rule things out you'll need to go have some tests done.
Personally, before going to the doctor, I'd take a look at what I was eating, like Hot Carl suggested. (Who refers to themselves at Hot Carl anyway?)
I'm assuming it's a reference to this:
https://en.wikipedia.org/wiki/Hot_Karl_%28slang%29It was referenced on South Park one time and that's where I heard it.