I've only just seen this thread and I couldn't go to bed without adding to it, even if you've gone to bed yourself.
I have two boys. DS1 had silent reflux as a baby and, I'm afraid to say, is still on ranitidine now at 2.6years old, although there is a major family history of reflux in adults, so I know we are bucking the 'they grow out of it by a year old' trend. He is now lactose free (after 4 months of being clinically anaemic, wight plateaued etc..and like your DS, improved for a month and is now going downhill again -why??!)
He had only been on a newborn dose of ranitidine until recently but was on heavy doses of preventer and reliever inhalers for the hideous night coughing (which cost me several friendships due to the near-depression it created - I really do understand how you might be feeling). They worked when he was well but as soon as got a cold, we'd be back to three hours of non-stop coughing and often up three times a night steaming him in the bathroom. (The bathroom is wrecked!) The coughing went on for 6 months before we got the inhalers. I turned up at the GP again, was 6 weeks pregnant and told them to do something - luckily they listened!!
Recently we've increased the ranitidine so that it is right for his weight and we have removed 3/4s of the dose of his inhalers -it's been amazing. I'm not sure he ever needed the inhalers, but we did, until we found a better answer.
Sadly, DS2 (8 months) has proper reflux (and has ruined the lounge carpet!) and we're limping along again. He actually slept through last night for the first time. I'm convinced that refluxy babies really struggle with sleep. DS2 is on a massive slope - it needs to be like a ski slope to make a difference I think. He's on omeprazole and domperidone as ranitidine didn't work for him. He arches so much in the daytime that I struggle to hold him. It can be heart breaking. Despite this, he's above the 90th for weight and people think I'm making a fuss about nothing (including the grandparents..) He also has sleep apnoea, which I think is linked in his case and is a whole different, scary ball game.
My ideas
Maybe you need to try ranitidine? Suggest it to the GP. They don't know everything, as I've discovered. Different children certainly seem to respond better to different drugs. Could you add in a dose of Gaviscon (which didn't agree with my two) in the night, as it forms a layer over the stomach contents so should help to stop it causing the reflux? Is he having a drink at that time of night which might be causing it? You could ask for some Carobel (a thickener we were prescribed for DS1 to add to drinks to hold the liquid down - I know he's not being sick but it still sounds like reflux symptoms) I was told that silent reflux is more painful than 'proper' reflux because the acid goes up and then down again, not just up and out.
Sorry for the epic post and jumble of ideas above. All I really needed to write was that you are not alone, you will make it through, (DS1 is testament to that!), even though you might wonder how at the mo. I'd say do go on holiday, but personally, I know in my heart of hearts, I might regretfully reduce the time away. I hope you don't have to. Cry on the GP, stamp your feet, make suggestions etc.. Get your health visitor involved too. Keeo going back until they give you something to try. It all takes energy, but it's worth it if you can.
In the long run, when I can see the woods for the trees, I fully intend to start a campaign of some sort to get reflux recognised for what it really is (and what it does to families in some cases) and to try and get it researched better. My GP reckons it's not looked into because mostly it never gets past the GP and because most children grow out of it.
Will stop now.. after sending a big unmumsnetty hug. Come back to us here.