I am constantly craving orange juice! i'm not hungry and not craving sweets or junk food. i drank almost a gallon today. why could this be?

Orange juice: Probably because you like it but a gallon a day is far too much. Have you given any thought to why you take so much OJ? Are you having to urinate several times a day? I suggest that you take your orange juice no more than twice a day (glass full, not a gallon) and if you are thirsty take water. Frequent urination from too much liquid is not good for you!