You might be a psychic vampire. When you were surrounded by people you could feed yourself pretty easily and have an OK living, but now you don't have lots of people around so you are starving. Some people are but they don't know about it.
This would explain the lack of vitamin D too. I'm not sure if sunlight will make you feel better though.
That is a good one, unlikely but something to think about OP as it does make sense! Look it up and see if you have anymore of the symptoms that match as there is quite a few from when I had a weird spiritual happening and many symptoms that did come up on my search of always being tiered, the most likely reason is that you are having to much sleep and not doing enough exercise or eating well enough.