Your carbohydrate threshold depends on your degree of insulin-resistance. The principal reason we recommend a limit of 20 g/day is that it is low enough to get everyone into ketosis, except for those who are especially insulin-resistant. Since elevated insulin interferes with ketogenesis and fatty-acid metabolism (not to mention preventing triglycerides from being broken down—lipolysis—so that the fatty acids can leave the adipose tissue in the first place).
I would strongly recommend dropping your carb intake from 30-35 grams net to under 20 g total. If that doesn’t work, you may need to drop your intake even further. The sleepiness is likely from too much carbohydrate—it’s the crash from the over-production of insulin because you are insulin-resistant. You can avoid the crash only by eating so little carbohydrate that the resulting glucose rise doesn’t spike your insulin so badly.
If you find yourself feeling lightheaded, dizzy, and having muscle cramps (you didn’t mention it, but just in case), that is sodium deficiency and can be cured by eating more salt.
Now as for the weakness and fatigue you are feeling, that is because your muscles are currently relying on either (a) an inadequate glucose supply or (b) ketone bodies, which they can use, but don’t do all that well on. What the muscles really want is fatty acids to metabolise, and there is an adaptation phase that takes the time it takes. The only way to get through it is to stay consistently in ketosis, and that requires keeping carbohydrate intake below your threshold. You will know you’re fat-adapted when your energy returns. At that point, your muscles will be metabolising fatty acids in place of glucose and ketones.
