no animal respawn

i have a really cool world on my game and i like it a lot.but i killed all of the animals and they didnt respawn,then after a few days they respawned again.then i killed them again and they havent respawned yet and it has been almost 2-3 months.can u please tell me what to do because i dont have much food and all i do have is bread and it only gives you 1 heart.please comment