My little one has recently switched from ready to feed formula to powder. I've noticed that half way through feeding he can sometimes become very fussy... kicking and waving his arms. I try burping him and then go back to feeding but it the fussiness continues . When laying him up against a pillow he shows that he still wants more and only moves a little. I get so many bubbles from shaking the bottle that I'm wondering if that's causing a lot of discomfort... if I don't shake it enough I get clumps... any thoughts?