Unexplained fatigue needing 10-12 hours sleep?

For the past month I have had moderate fatigue, needing 10-12 hours sleep, still feeling exhausted and needing to nap around 4-5pm. I've also felt physically quite weak, unable to concentrate (fuzzy)and irritable.

No diet, sleep pattern or stress changes.

I went to my doctor, who suggested it was iron, and took two blood tests (a nonfasting then my blood sugar came up a little high so I went back for a fasting one). This came back with normal results, and my doctor didn't suggest any cause.

I've felt better the past 3 days thankfully! But I am wondering what it was or if it will come back? Also in these three days I've had itchy skin all over, I don't know if that's related.

Is it possible it was a virus that only manifested itself in fatigue? What virus could it be and are there future implications from having that virus?