instamessage chat history not restored

recently i successfully installed iOS 7 on my iPhone 4 using itunes restore method. before that, i made a backup of my phone including all settings, apps and their datas etc. there were some chatting apps like viber, wechat, path, instamessage etc. after restoring the backup from itunes, all app datas were restored except instamessage. its all chat history was gone which made me so angry. i don't know what was the problem. i made the backup successfully, so i don't find any clue. plz guys tell me how can i restore instamessage chat history?