Nausea during sleep. Clearly about this?

Hi, for lastone month my son has nausea feeling and vomiting. Initially he started with nausea only saliva comes that time. After few days he vomitted and diarrhea. We have consulted many doctors and they are diagnosing him for acidity. Now he is not vomitting but he has that nausea feel once he started sleep. After a minute he get into sleep or close his eyes he is getting bthay nausea feel. I am really worried and wondering why he is getting nausea feel and he is struggling to breath for a minute at least. I have asked this question many doctors but they don't have answer. Only answer is stomach infection. Can someone please explain me clearly about this? I couldn't see him while he doing like that. Feel like crying. Literally he is struggling to sleep. I am following below medicine for acidity Rantac 75 mg, Domstal syrup and duphalac for constipation. Still he is not recovered. He is active rest of the times. Only during sleep he is doing like that. Kindly help me.