Hi RT93,
Short answer: Based on your previous weight loss success, your current weight, diet, and exercise, I think you might have a metabolism problem. Get someone to check out your thyroid hormone levels and specifically your freeT3 which is the active thyroid hormone and is found to be lower in people who have been on extreme calorie restriction diets. Look up info on "Biggest Loser syndrome", see if you think you might fit that profile.