Most likely he is getting spoiled by the bottles because the milk comes out faster and nursing is harder. I would try harder to BF him more and bottle feed him less or not at all.
If you are concerned about whether he is getting enough, have your LC do a weighted feed. Though, if he is gaining fine, he's probably getting enough.
BFing can be hard, it won't always be easy and they will go through stages of nursing less, nursing more, longer, shorter, etc.