Yeah workouts really suck the first couple of weeks at sub 50 carbs.
Increase your carbs. De-novo lipogenesis (DNL), which is the conversion of carbohydrates to adipocytes, does not increase with carbohydrate intake unless said intake exceeds overall energy expenditure. Fat is good for low-intensity exercise, but worthless for high-intensity weight training or cardio. Here is a link supporting my conclusions: http://www.ncbi.nlm.nih.gov/pubmed/10365981