Grain problem?

I just started this journey of trying to figure out if I’m insulin resistant. For background, I’m a good weight (have always been thin, sometimes underweight, but generally good weight most of the time), exercise 4-6 times per week and don’t eat any processed foods or added sugar because of an MTHFR gene mutation and suspected corn intolerance. I had two bloodwork’s showing I was prediabetic (5.7 A1C) which was confusing given my lifestyle. I got a cgm to try and figure out wtf is going on.

After having it a week it seems like I can’t tolerate ANY grains. I can’t something higher glycemic like watermelon or a banana and be fine but having some oats or rice sends me skyrocketing (like 170, obviously not high for a diabetic but for someone who’s not supposed to be that seems high). Again, the only grains I eat are not processed and not white- ie fresh baked sourdough, brown rice, oats, quinoa etc. all of it seems to mess with me. Does anyone have this problem?? I’ve gone grain free for the past couple days and have been able to stay under 140 glucose for the entire day which is great but I’m STARVING