I have pre-diabetes, probably because of my years of eating Taco Bell daily and not exercising enough?

I read in Prediabetes for Dummies that I can't have diet soda anymore. I'm wondering what it is that I can eat. Also, I'm thinking this pre-diabetes is the cause of my fatigue and lethargy? What do I need to do to prevent more severe complications. I'm willing to cut out all sweets, but what can I eat?