The beginning is quite hard. An alakazam with psybeam was my first trusted pokemon in my team, a little squichy but his speed with his special attack wipe almost everything.
But before that, i changed 2/3 mons in my team for some other who the gym leader was weak and push them to the lvl cap too.
The game will come easier once you hit mahogany town and the move's eraser, and beat some more gyms for better moves.
Try to seek for mons with a lot of speed, they will attack sometimes twice before the first attack from the others mons. (Dugtrio, electrode, scizor, ninjask, etc...). Or mons with nice def/spe def with moves that heal them (fire punch, giga/mega drain, etc)