@SC: Stimulants can actually make you feel tired (though note you haven't gotten rid of them, unless you're drinking decaf tea -- a cup of green tea usually has at least as much caffeine as a cup of coffee ), especially after a few hours, it takes energy to process fat and sugar* (also, neither of the two are particularly good for get-up-and-go energy, heh -- they're not terribly good for pep, despite what common narratives say about sugar), and if you're exercising and losing weight, you're carrying less around, on top of all the other good stuff a jogging regimen brings. Just to name a non-exhaustive list of what's going on, heh, as metabolism and whatnot is pretty complicated stuff. Basically you're doing most of what naturally increases personal energy, so... that's what's happening.
*Though I wouldn't be entirely surprised if you haven't really cut back too much on fats and sugars, heh. They actually tend to largely come from stuff that isn't immediately fat or sugar, hah.
The 'energy' stuff that the idea of a sugar rush comes from is a confusion of terms. Food/metabolic energy is energy in the way physicists/most other natural scientists talk about energy. On the other hand, pure caffeine has zero or
negative energy in that sense.
If you mainlined glucose, you wouldn't be any more
alert, on the other hand, unless you're in the middle of falling into a hypoglycemic coma. You couldn't do much running without sugar, either, you'd get tired fast - but it's more of the 'halp my muscles are jelly' kind of tired, not 'I gotta go inhale the pillow a bit' tired.