I recommend finding a good, well-rounded multi-vitamin as well as taking EFA's (essentially fatty acids). But yes, examine your diet thoroughly. A poor, unbalanced diet that is devoid of good nutrition will leave you feeling tired, sluggish, and well...pretty much crappy all around. Now, should you deprive yourself of all indulgent things? No. Everyone should be able to have a piece of cheesecake or whatever every now and then. The key is moderation.