For most libido issues are related to low fat diet or stressful situation,
reducing calories too drastically will induced a stress response (read cortisol increase), overtraining will obviously do this too so maybe look at your training, it might not be conducive to a low carb lifestyle.
if your not over training or overly stressed than increase the cals for a little while from fat and see if that helps before resorting to supplementation.
EDIT: this is all assuming you are fat adapted and not participating/competing in aerobic activities! if this is the case low carbs may not be the best option for you!