Originally Posted by DrIsotope

For me it wasn't carbs at all, but protein-- that is, not getting enough of it. I assumed I was sufficiently refueling after rides, but would have persistent fatigue and muscle soreness. I had started using the MyFitnessPal app to track calories, and it changes macros based on exercise-- and on days when I would do big rides, it would recommend I intake what I thought were ridiculous amounts of protein-- like +200g per day. But they were right. I try to take in +100g of protein a day (I ride daily) and I am far less fatigued and the chronic leg soreness is gone. Greek yogurt is now one of my go-to snacks, because I can get 12g of protein for all of 100-120 calories.

I recommend the app, as well as increased protein intake, along with just you know, riding more. 4-6 hours a week isn't much, unless the training is extremely structured. I don't do any sort of structured/timed/interval training, but my last century was 108 miles @ 19mph. I just ride a lot.