There isn’t enough information in order to come to a conclusion, or to offer advise. I also don’t want to assume anything, either.
How do you classify your dietary lifestyle?
How long have you been incorporating fasting into your lifestyle?
Are you fat adapted?
What was your longest water fast up to this point?
How would you describe your breathing pattern?
When I eat food I get that empty achy feeling in my stomach the next day. Especially when I eat late at night. After a day of fasting or liquids it goes away. Try and push it to the second day and you should get relief