You can call Bianca via Xtranceiver to see how happy a Pokemon is.
here are the levels of happiness (least to best):
Hmmm... It may not like you very much. By any chance, you... Are you a very strict person? I feel that it really doesn't like you... (0-49)
The relationship is neither good nor bad... It looks neutral. (50-99)
It is a little friendly to you... That's what I'm getting. (100-149)
It is friendly to you. It must be happy with you. (150-199)
It is quite friendly to you! You must be a kind person! (200-249)
It is super friendly to you! I'm a bit jealous! (250+)
Raising happiness:
Give it items
let it hold the soothe bell(which you may not have)
use him in battle
Dont's:
Do not allow the Pokemon to faint in battle
Do not use bitter items on the Pokemon
Do not keep the Pokemon stored in the PC
Do not trade the Pokemon