Talk to Gastroenterologist on Stomach Issue

My issue started around 6 months ago. I started feeling very bitter and bad taste in my mouth and burning tongue. 2 different doctors advised Nexum tablet for 1 week. but after 1 week problem came back. Overall digestion is OK i feel hungry. i dont have constipation or diarrhea. i dont have acidity. Since last month, i feel so much weight and heaviness on my chest and my heartbeat gets too fast. I visited local doctor and he said its not heart issue it is because of stomach problem and advised Nexum again. He advised CBC and TSH. Both test reports were normal. Now, since yesterday. my tongue is so sour and burning and stomach is aching and i dont feel hungry at all. Pls guide what is the issue. advise any lab tests if required or any medications for permanent treatment.