0 Carbs will both make you fatigued and increase fat loss. However, it is not recommended that you cut out all carbs because certain functions (ie; the brain and eyes) require glucose, which only comes from carbs (sugar).
If you are not engaging in extremely intense or long duration exercise (HIIT or long endurance), you may cut your carb intake to 2g/KG bodyweight. All your carbs can come from fruit, and low GI fruit would be even better, like berries. After 1 week of adjustment, you should feel less fatigued and moody!
Regarding your knee- this is a whole different discussion; I can't give you an answer since I have no idea what is wrong with your knee. There are a hundred things which could be going wrong, and nearly all can be fixed up with a good athletic therapist, osteopath or physical therapist. Fix your knee and then engage in the most effective leg exercises: heavy squats (front and back) and deadlifts. Those two exercises cover every single lower limb muscle!
Good luck to you!
