Why do I have no appetite suddenly?

I’m on the slimmer side of average weight for my size (5’6”, 116 lbs.)
I usually eat….well, not a LOT but a healthy amount of food.
Lately, I haven’t been able to eat much at all.
I haven’t had much of an appetite, either.
Yesterday at work I got a chicken quesadilla and could literally only finish one slice. Normally I’d eat the whole thing but that one slice made me feel STUFFED. It felt like I ate a three course meal. I almost threw up.
Nothing tastes good any more. It kind of feels like I’m losing my ability to taste, as odd as it sounds.
I keep trying to eat regardless of how awful it makes me feel because I know I have to. It’s getting harder though.
What could this be? What can I do?
I also feel exhausted every day, even before the appetite loss.
I eat healthy and sleep as much as I need to.