I had to add to Able’s post as I do have personal experience with this. I was just recently diagnosed with hiatus hernia and most of the stomach symptoms you mention I do have. I often feel nausea after drinking water or eating larger meals etc. Your acid reflux could be caused by HH as well. But I do see that you had a gastroscopy (called endoscopy in US) done which this is how HH is usually diagnosed (mine was). I wonder if they missed it, it does happen if they are not looking for it. I have reflux but mine was caused by reduced size of the stomach and not closing up properly due to HH so the food and liquids come back up. I also have some chest pain and pressure which is caused by the stomach problems.
Watch out for mineral water. I see you are in Poland and it may be similar as in Bosnia that all mineral water is carbonated. While it might make you feel a bit better momentarily, 2l of mineral water also burns your stomach and creates other problems, plus adds some toxins to your body as well. I would reduce it or stay away from it completely. I feel better on just plain water left in open container to get rid of chlorine.
Reflux is tough if you take in a lot of liquids and don’t take enough solid food to “collect” excess water and acid as the food and acid is refluxed back up causing discomfort such as nausea and heartburn. Having a lot of liquids which is required for your treatment is tough so try following few things to make it easier:
– don’t drink lots of liquids near your meals
– split up your food into 5 or 6 smaller meals
– when you drink liquids, drink it in smaller sips vs. gulfing down a glass of water (I used to do this)
Lemon water was also tough on me as it was generating more acid and giving me more discomfort. I have it in the less water and in the middle of my meal so that food takes it in. I have my kefir with dinner and I usually have my meal, then drink lemon water with my supplements and finally drink kefir after it so kefir soothes it.
Hope these few tips help you.