Not to pile on, but hopefully another voice can drive the point home. You are not eating nearly enough. You’re basically on a starvation diet and trying to train on the bike. You are not overtrained, you are vastly underfed.
Vegan of 5 years here. It’s not quite as easy to get calories without animal products, but it’s still possible and you have to do it or you’ll wither away.
Example of a day of eating for me…
Breakfast: Shake that includes 1-2 bananas, rice milk, protein powder, peanut butter powder, berries, spinach, flax seed, chia seeds. It’s like 30oz of shake. Huge. Usually will have something else as well like a few pieces of toast and jam/vegan butter or a bagel or some sort of carb source.
Morning snack: Fig bars or similar.
Lunch: 1 cup (uncooked) rice (which is a lot of volume of cooked rice), an entire can of black beans, 3-5 medium tortillas.
Afternoon snack: A bagel or a couple bowls of cereal, or a quick frozen noodle bowl thing. Depends on the day. Usually have another protein shake with soy milk somewhere in the day too.
On the bike: Maltodextrin/fructose mix. 120g+ carbs/hr. That means for a 3hr ride it’s well over 1000 calories just in on the bike fuel. Immediately off the bike I’ll have another protein shake with peanut butter powder and rice milk.
Dinner: 3/4 lb of dry pasta, veggie sauce that might have 2 whole squash in it and a whole jar of tomato sauce.
That might not even tell the whole story too, as I’m always grazing on other stuff throughout the day and in/out of the pantry. You probably look at that and think it’s nut, but I’m at 7% bodyfat. Cycling burns immense amounts of calories that need to be replaced and used by your body to get stronger. If they’re not there to burn, you’re gonna feel like shit all the time.
I don’t think you need weeks or months off to get out of some deep training fatigue state. I think you need to track your calories and eat 3-4k a day for a week and you’ll feel amazing. It will feel like you’re eating constantly, all the time and you’ll probably feel stuffed a lot too. That’s fine. You need to start choosing calorie heavy and carb heavy foods too. There’s 113 calories in 1lb of arugula. So to get 3000 calories you’d need to eat 26.5 pounds of it. That amount of arugula would take up an entire fridge and if you spent the whole day chewing it wouldn’t be possible to get through. To contrast that, 1lb of peanut butter there’s 2600 calories. Pretty doable to eat an entire jar of peanut butter in a day if you ask me.