To really succeed, IMHO, you need protein. Getting your body to switch to fat burning for energy vs using carbs will allow you to perform at a more consistent level over a longer period of time without fatigue/cramping.
I used to do cross country in hs, and did some competitive running as an adult in my mid 20's. I noticed a marked improvement in my performance once my body switched to fat burning over using carbs.
For someone like you who consumes a ridiculous amount of candy this is likely not possible though. You need to really cut carbs to force the metabolic change.
I'm not running to lose weight.