Hi. I actually asked my Doctor about when to give, as I remember, she prescribed it before a feed and the pack says after.
My doc says it doesn't really matter, that as long as it is taken close to feedtimes, then it will thicken the milk in the tummy. I think expressing and giving through the bottle is a huge palava to be honest and not very convenient either! If you find it easier to give before, then do, I'd give it immediately before feeding.
Then try to keep your son upright (i.e. I guess you are holding him so he faces over your shoulder?) for as long as you can afterwards (min 20 mins). It is a faff, especially in the night, but it really helps. If you think that the valve to the tummy that isn't yet mature is open, so it is a bit like laying down a bottle with the lid off. My DS only fell asleep in the upright position in the first couple of months, he cried as soon as we tried putting him down (where the acid kept going back up, which we didn't appreciate at the time). He used to fall asleep sat upright over our shoulder, then wake in distressed crying from the pain. It broke my heart and no-one can truly understand what it is like unless you have a baby with reflux yourself. But it does get better, but I think it is one of those things that you have to push for with the doctors (particularly if your baby is gaining weight well, which my DS also did).
In many ways, it is good that they don't intervene too much - the valve maturing is a natural process, so there isn't anything 'wrong'.
Don't worry about people cooing over him and then backing off. The people who really matter won't do this. I used to just warn people that he is a 'sicky' baby and if they bounced him, I'd say 'it's at your risk' jokingly. One woman from antenatal said to me 'oh that must be annoying, I haven't even used a muslin since i gave up breastfeeding in a really smug way'. There was me with like a stash of 6-8 muslins to the side of me gritting my teeth!!
I promise you, it will get easier, you will begin to predict those noises that happen just before being sick, you will become expert at catching it at the right time!
I hope the Gaviscon works. It is a faff, but if it works for you, then it is worth it. Good luck