I was going to suggest you look at hypothyroidism, too. About 1.5 years ago, I was tired all the time--could sleep 12 hours at a time if my kids would let me!; I couldn't lose weight no matter how little I ate; "lethargic" would've been "spunky" for me!; my hair got very dull and thin and my emotions were (still are) out of whack. It came out of nowhere, too. The only way you'll know if that's it is with a blood test.
You know, though, this time of year, when it's rainy most of the time and you don't get enough sunlight; you can get weary from the lack of vitamin D and B. Try taking a multi-vitamin.
We're all doctors on here, aren't we?! We all act like we can diagnose anything you throw at us.....ONE of us has had it at one point or another!