Well, I can tell you one thing that will give you fatigue. Sleep apnea. And apparently diabetes and sleep apnea are associated. But anybody can have it. And it isn't just about weight, sometimes it is just the genetics of your throat, tongue and mouth. I've struggled with fatigue for some time. And while I would certainly urge you to heed the advice to get you thyroid checked, I had extensive tests, it would be worth looking at your sleep.
I went to a sleep lab and found I was waking over 30 times an hour and I stopped breathing a lot, at one point I didn't breath for nearly 3 minutes. I never reached full deep REM sleep and was always tired. I got treated with a CPAP machine and it did help. It didn't solve all my fatigue issues, I still have a significantly low body temperature and fatigue symptoms, but I am clearly better.
A good home test if you sleep with someone is to simply ask them to observe you sleeping during the night. If you stop breathing, it is pretty obvious. You may never notice, you are asleep and if you and your partner are always asleep at the same time, your distressed sleep may go totally unnoticed.
ps. My sleep doctor didn't advise weight loss as helpful since I am at a healthy weight already and a 10 lb weight loss only gave like a 10-20% improvement on average.