Alright first of all dont get disappointed when you get bad level ups because this game has low growth rates(at least most of) and enemies in this game weak compared to other games. Also number of the master seals in this game can be problematic. Because there is not too much or some of them near end of the game. So using pre-promoted units can be useful. Like Wolf and Sedgar. They are great units ıf you reclass them into generals. Because their growth rates around 80-100.
Also you are at the beginning of the game how did you manage to make your units underleveled?