It's very simple.
Our taste buds send signals to our brain, in turn, it releases insulin as a pre-emptive strike to clear out any glucose in the blood stream. Especially for something that's several hundreds of times sweeter than sugar like stevia, or artificial sweeteners.
If you're fasting, or just woke up, this takes the tiny bit of glucose out of your blood. You instantly feel hungry because there's no actual macronutrients in your tea, so your body says Ooops! We need more food now, brain's in danger.
If you don't eat, you'll go into gluconeogenesis via cortisol signaling. So you're better off avoiding all sweeteners if you're trying to cut down on calories.
You'll get fatter if you consume zero calorie foods that are very sweet.
Your best course of action is to break your addiction to sweets. You can use L-Glutamine for this. Anytime you feel a craving to eat, have a little bit of it. ALA can also help.
The better path is to become fat adapted and get into ketosis - doesn't have to be all the time, but once you're adapted to burn fat, it's no longer a problem. One thing that can help this is black coffee as it shuts down hunger, and to add extra virgin coconut oil to it (or have it bulletproof.) Don't over do this as the fat calories do count in the long term, however, if you do it just right (remove fat from elsewhere when you use this), it can cut down your appetite. Best yet, since caffeine and coconut oil do not trigger an insulin response, as long as you don't overwhelm your system with it, your fat cells will open up and release their fat stores so you can burn them.
Insulin prevents fat cells from releasing their stores. So as long as you eat anything sweet (even zero calorie), or even proteins (though to a lesser degree due to glucagon stimulation), you won't burn fat.
Learn to love your coffee black - if you can't drink it black either you're not used to it yet, or it's really crappy low quality stuff and you should find a better brand.
Look into intermittent fasting in the mornings, bulletproof coffee, and carb backloading at night after work outs.
If you're not trying to lose fat, just use a good sweetener, like a high quality maple syrup, or a good unfiltered local honey. BTW: avoid agave nectar - organic or not, it's pure fructose, even more so than HFCS.