TonyReid

Being that new to carnivore the most logical reason you were have energy issues is your body had not adapted to burning fat for energy. It was still wanting carbs to burn.
It can take some time before we become fully adapted and until it happens you’ve just got to tough it out. It’s part of what many in the community call the keto flu. Some people don’t do well going cold turkey into carnivore and need to ease into it by being keto first and then tapering down to carnivore. I’m a jump in with both feet kind of guy so I went hard core from the beginning and I experienced what you did but I just powered through it.
As far as the weight loss and you being already slightly built the question would be what is your built like? You may be slim but are you an athletic built slim or are you a weak slim. If you are skinny-fat then it would make sense that you were losing. If you are athletic then you may not be eating enough.
To calculate protein needs, one should aim for approximately 1 gram to 1.2 grams of protein per pound of lean body mass and an equal amount of fat. This approach is suitable for individuals seeking to maintain or gain weight and muscle mass. Protein requirements may vary based on factors such as age, activity level, and individual metabolic health.
Fat (or lipids) - 9 calories per gram.
Proteins - 4 calories per gram

Now I never counted anything myself. I just made sure everything I ate was cooked in animal fats and any rendered fat was poured back over the meat like a gravy. If the meat is lean then I’ll eat butter with every bite of meat.
Good luck and welcome to Carnivore Talk.