Simple carbs break down into Sugar very quickly and with your refreshed digestive system, you may just be noticing it for the first time.
Processed foods are full of sweeteners as well. When we eat them all the time, we don't notice it. Spaghetti sauce doesn't need sweetening beyond the natural Sugar in ripe tomatos, but if you buy it in a jar, chances are that it has sweetener added.
Fruits and many veggies are naturally sweet. Make sure you eat a balance of dark green veggies as well. They offset the sweetness with a hint of bitter.