I have suffered from a petic ulcer in the past, and that felt like being full despite not eating.
Does the pain come in waves that last for an hour+ and does it go away if you lie or sit a certain way?
Does it go away if you take ant-acids? (heartrburn tablets)
in anycase, not eating for long periods wont do you any good. Stop any exercise for 48 hours at least and see if it improves, other than that hot foot it to your doctors