I believe we have energy the first week or two of keto because we are using up the glycogen stored in our muscles. In that respect, we are still carb burning, using a fuel our bodies are used to. Once those glycogen stores are depleted, we have to start utilizing fat for energy. That is when the feeling lead-like and sluggish begins because our bodies have to learn to use the new fuel. That takes many weeks.
You have used up the glycogen stores and now adapting to fat burning, but I think the reason you are especially tired and sluggish now is because you are most likely not eating enough. I found that my hunger signals changed on keto. Your body may be telling you it needs more food, but you may not be recognizing the signals. I used to get shaky and headachy when I was hungry. Now I don’t “feel” hungry, but I will just get to the point where I can’t stop thinking about food.