Have you tried changing your fasting window? Are you getting enough calories? Are you sleeping well? I’m just trying to go through a mental list of all possible things that could make you feel lethargic. You’re not eating carbs, as per your meal description, so it’s not your food choices. Have you tried splitting the meal in two? Eating half of it at 13:00 and the other half a bit later? I feel that way sometimes too, and I don’t eat carbs either. I find that if I don’t eat enough fats in my meals, my energy slumps.