There could be a few different things at play. I'd try a bit of sea (or himalayan etc) salt and see if that helps. Otherwise, perhaps you really are just hungry and need to eat. Many people doing IF do larger meals with minimal snacking (since part of the benefit is to keep insulin low most of the time). Higher fat content and lower carb content in the meal before a fast will also help.
It may also just take time for you to work your way up to longer fasts.
It may also just take time for you to work your way up to longer fasts.