Why do we have cravings?

Cravings can be because of two reasons, either stressful situation you are dealing with or your last meal was not filling enough. So either your body is asking for comfort food, or your meal was not meeting your requirement of either taste or nutrition, or both.
What you can do is, if stress in life is making you crave then deal with your stress with a change in your attitude, not comfort food. Learn to cope with it, learn to deep breathe to help you through situations. Try turning to prayers and/or meditation to bring peace to your mind. We all have our share of stressful situations. We have negative people and situations around us. Focus on the positive aspects, on the people you love, on the things you cannot live without and also on small sources of happiness around you.
If your food is too bland or you didn't get filling feeling, then increase the portion of salads and vegetables and also try different condiments and flavours to make your food more interesting and tantalising to your pallette. Add interesting dressings to your salads. Vinaigrette dressing is healthy and weight loss friendly.
Your cravings can be for sweet or savoury. You can make your food taste according to your craving for savoury. For the sweet you can sometimes have a date and two almonds.
Having said that a couple of small bites of dark chocolate will do more good than bad, once or twice a week. Indulge!