Just wondering if anyone has any experience with reflux in toddlers?

My DS is 20months and I very strongly suspect he has reflux. At about 11 months old he started vomiting a lot, big huge choking vomits, and at 12 months I went to see our MCHN. She was utterly useless, wouldnt talk to me about signs of reflux and where to go for help and said it was likely a viral illness
So we went to see our GP ..... half a dozen times! No one would listen to me saying I think its reflux, as soon as they asked about his weight and I said he was gaining fine, they stopped asking questions and said he is fine. I did eventually get a referral to the public pediatrician through my nagging, and we waited SIX MONTHS for the appointment That was in August, by which time the vomiting had eased a lot. I still went to the appointment and discussed everything with him, and he said it was likely reflux causing the issues but now that the vomiting was easing it seemed to be taking care of itself so there was no point looking into it further.

But here we are now, and its still giving DS a lot of grief. He is a HUGE comfort feeder overnight, which is why he has still gained weight. BUT, he has had HUGE MASSIVE weight gains because of it. He was 11kilos at 12 months, now at 20months he would be close to 17 kilos. At 18 months he was 15.5 kilos, MCHN had something to say about it and said the pediatrician would too. The pediatrician bless him wasnt concerned at all about it though and said he will even out. But I am worried again.
I can hear him doing big swallowing when he wakes at night. Only a breastfeed will get him back to sleep so I suspect its easing his discomfort as he gets really upset when I try to get him to back to sleep another way. Basically having looked at the reflux website, he has had basically ALL the symptoms of reflux (more so earlier in the year, but still showing a lot of symptoms at present).

We did get losec tablets when he was 14 months old, they didnt work as he also had an ear infection at the time and our dr said to stop them. But I still kept the box, and a few weeks ago started him on them just to see. He responded positively, he started waking less at night and was easier to settle. I stopped them over a week ago, and he is back to super wakeful nights and being hard to settle and the last few days has started vomiting again. There's no rhyme or reason to his vomits, they come randomly after a breastfeed or food or after he gags/coughs on nothing.

I guess I dont know where to go from here. I am going to book in to see our GP again for asap, and will likely demand a referral to a private pediatrician. What sort of testing can they do? Will they even take me seriously for testing considering reflux isnt so common in older toddlers? For a long time after our repeat dr appointments I thought I was imagining symptoms, and just kept plugging through to the specialist appointment. But now its all starting up again I KNOW I am not looking too much into things :/