Why am I having unusual food cravings in pregnancy?

No one knows. Weird food cravings are common in pregnancy. Some people even crave non-edible items (PICA) like dirt. It is ok to crave and eat different foods in pregnancy as long as they are healthy and as long as they are actually food substances.
Who knows? . Food cravings or aversions have been not been shown to correlate with a physiologic need during pregnancy or at other times. Maybe it's psychological. The important thing is to follow a healthy diet while pregnant to give your baby the best possible start in life. See http://www.Webmd.Com/baby/features/coping-with-pregnancy-food-cravings for an interesting discussion of this topic.