1. You think you're eating healthy, but aren't.
Does your diet consist of a massive amount of "products"? Low-carbohydrate or not, you want to eat real whole foods. Litres of diet soda, plates of pure fibre in the shape of noodles, and loaves of 1g net carbohydrate "bread". You're just feeding an addiction and consuming empty calories - sound familiar? Disregard the labels and look inside for what you know to be true: this crap isn't food, and you shouldn't be eating it.
2. You're under too much stress.
The stress response system is subconscious; it responds to stimuli and nothing else. Emotional stress, physical stress, financial stress, relationship stress - I hesitate to even make these distinctions, because the body does not differentiate between sources of stress. They all cause the body to produce cortisol, the fight-or-flight hormone that catabolises muscle, worsens insulin resistance, and promotes the storage of fat. For 200,000 years, stress meant a life or death situation. It was intense and infrequent, and the cortisol release was arresting and extreme enough to improve the chances of survival. Today, our body responds to a stack of paperwork the same way. Traffic jams are like rival war bands. Take a step back from your life and take stock of your stress levels - they may be holding you back.
3. You're not getting enough sleep.
Chronic levels of sleep deprivation cause the release of cortisol, our old fat-storing friend. The biggest spike in (fat-burning, anabolic) growth hormone plasma levels occurs in deep sleep. Recent sleep studies showed that irregular sleep patterns are linked to weight gain. Get seven to eight hours of solid sleep a night.