How many grams of sugar should i get?

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I'm prediabetic. Or at least i figure i am, it runs in my family (on bothsides) i'm obese and i used to eat a ton of sugarry foods. Google has left me wondering, and i really can't afford to go see a doctor right now.

To put things simply, i'm 5'4, i weigh 267 pounds. at the moment i'm eating 1680 calories a day. I get about 1 hour of exercise a day (usually walking) I eat 3 servings of veggies a day and 3 servings of fruit. And of course whole grains, low fat cheeses and meats.

I typically only get two portions of added sugar. One is 1 tsp in the morning for my coffee. The other is anywhere from 10-20 grams in a serving of 100 calorie snack cake, or 120 calorie frozen yogurt. Everythign else is natural (in fruits, veggies, milks, etc) so while i only consume 15-30 grams of added sugars, i end up with 70-100 of natural sugars.

I have tried cutting down my fruit and added sugar intake. It seems that my body relies on the sugar, ebcause if i don't get enough of it i get hypoglycemic. (or whatever the term is when you get shaky, your vision blurs, you get iritable and dizzy) I don't know what to think.