People who know me from other places may say I'm a broken record, but it needs to be said/asked: Are you counting calories? To say that you're "eating better" is great, but let's face the reality that you can still overeat with healthful food. (And it doesn't take drastic changes to add a few hundred calories per day.) Despite what we've been told, exercise does make us hungry (as it should), so it's very easy to go for a ride/hike/whatever and end up overeating later to compensate.

About the fatigue, well, it's hard to say. My initial bet is on dehydration. Are you drinking enough before, during, and after your workout? Sorry to be graphic, but the easiest way to check hydration is pee color. It should be virtually clear. You may also need electrolytes, but I don't know how to check for that.

It is possible that you're working a cycle (pun unintended) where you work hard, don't compensate soon enough for the calories burned, are fatigued, then overcompensate with too much food and too little movement later. But I'd check for hydration first.

Last thought: Are you alternating hard days of exercise with easy days? You can actually recover better if you exercise lightly the next day.