Hi, Stomach bloating or pain or belching could be due to acute gastritis,dyspepsia,Erophagia,irritable bowel syndrome,peptic ulcer,bowel obstruction,inflammatory bowel disease like crohn s disease or ulcerative colitis. As you are taking tab.Nexium since long time for GERD for symptomatic relief but the important thing is to diagnose the cause of this beching,gas or dull ache inside stomach since for 1 week. You should undergo certain blood investigations with urine and stool examination for R/M and ova or ultrasound of abdomen or upper GI scopy if required. Treatment is mainly depend on the underlying cause but symptomatic treatment can be given. You may require antibiotics (quinolones, antiprotozoals or amoxycillin derivatives) and anti-helminthic (albendazole) with proton pump inhibitors and prebiotics and probiotics . You must consult your gastroenterologist for detailed medical history and thoroughly clinical examination and get it diagnosed first. Thanks.