I feel like sugar in general makes me tired and makes it difficult to concentrate. Sometimes (though rarely) I consume sugar in the evening to make me tired.

I can't help but eat candy if it's available, so I just learned not to buy it in the first place.

From personal observation (I think it is even backed by research) not having enough sleep causes craving for sweets/junk food.

That's a bit too generic I believe.. What if you don't have a sugar/junk craving in general due to diet? i.e. keto

Sucrose is what bees crave so its pull must be deeply embedded in our reward system. I associate the high sugar consumption with short circuiting the reward system.

I had the same habit. You eat sweets -> blood sugar goes up and you feel energetic. Problem is, it also goes down very fast, at which point you feel sleepy and hungry at the same time.

Really easy to become overweight this way.

Then you get diabetic and your blood glucose levels don’t fall off as fast anymore, which solves the problem in its own macabre way.