missVN it does sound like reflux related to me, I would also make sure that the flow isn't too slow as the Gaviscon can make the milk really thick and hard to get through the teat. It might be worth trying SMA Staydown instead of Gaviscon to see if it helps?
Sorry you're having a tough time, are you doing all the usual stuff like propping up his sleeping area, his changing mat etc. and keeping him completely upright for 30mins after a feed. Keep him as upright as you can during a feed and if it helps him put some music on and stand up and gently rock him, sing to him etc. anything to keep him calm As soon as he starts to fuss take the bottle away and gently rub his back and wait until he's settled before offering it again.
He might do better with more frequent feeds - every 2-3hours instead of 3-4, the reflux might not bother him so much with smaller feeds?
Hope it gets better soon
xx
To everyone else - sorry I haven't been on much, I'm coming back to read through and catch up with everyone later xx