Hi Renee

Your baby does use a little less energy feeding from a bottle than he would feeding from the breast however, if he will not take a bottle then there is no point in doing this. I think that you should give sleep, feed, play, feed, play a go. Trying to force your baby to take a bottle or a sippy cup will only cause him more stress and thus cause him to burn more energy.

Another thing to consider is:-
Has your baby become more active recently? If so this could explain the reason for the lack of weight gain. I would not be overly concerned at this stage. See how things go over the next month.