Hi There! I've Been Feeling Tired For A Few Months

Hi there! I've been feeling tired for a few months now. 4 days ago I started a diet. It's more of a healthy eating, no sweets, no bred... basically cutting down on carbs... Up until I went on that diet, I also drank 1 or 2 beers every evening, but now I stopped those too. Today I woke up very tired. It's like I've been drinking till 6 am and then gone to work... and I've been feeling like that all day... What can it be?