Ah, poor pet, reflux must be bad
how old is he?
What sort of dose of the reflux mess is he on? High for his weight? Reflux meds need review regularly in the early months and often the ones you start with don't do the job and different meds are required. If he's still not eating, or gaining, I'd be back off to the doc to get the meds reviewed. Have you seen our reflux board? Loads of helpful and experienced ladies there who can give some more specific advice.
Pulling and chewing can be a sign of lack iof milk but can also be LO's way of trying to slow a letdown. My son used to clamp down on the breast and shake his head like a dog with a snake and that was when I was letting down during a feed. OS can make reflux symptoms worse too.