The fact that he is still so fussy about feeds suggests that the reflux isn't under control and that is more than likely having an impact on feeds and sleep. Gaviscon is only a milk thickener (I'm assuming you are UK and on infant gaviscon powder) and doesn't help acid reduction so I would take him back and see if you can get meds prescribed, Ranitidine (zantac) is usually the first choice for babies.
You could also ask about trying a hypoallergenic formula instead of the lactose free one, lactose intolerance is very unusual in babies, but cow's milk protien intolerance is much more commonly a cause of reflux.
{{HUGS}} it's really hard, I have two refluxers so feel your pain.
Laura