12 days in is an average time to have switched over from being a sugar-burner to a fat-burner, which means you are using your own body fat stores for energy, or your "on-board pantry" as Dr. Westman calls it (that's a good thing!) If you only eat one meal a day for a while that is OK, many go through a period with little hunger and then your appetite will adjust as Rob wrote.
Are you on any diuretics? or other blood pressure or blood sugar medications which may need adjusting? Are you drinking enough water to keep hydrated? In addition to the extra salt, you may need extra water. Are you in the UK where there is a "heat wave"? Think of other reasons beside the change in diet as well. All the best,