Hi,
Welcome to health care magic,
Stomach pain could be because of dietary origin like
food poisonings or infection like
gastroenteritis but needs to be evaluated further by various investigations.
Here,it is likely due to spasmodic pain as you said pain gets worse when you sneeze,cough or even breath.
You should go for routine blood count,ESR,urinalysis with ultrasound abdomen with to rule out other gastric pathology.
You should be given,
1) Antibiotics (like ofloxacin with ornidazole).
2) H2 blockers like ranitidine or
proton pump inhibitors (like
pantoprazole,
rabeprazole etc ) with cytoprotective drugs like sucralfate,misoprostol etc.
3) Antispasmodics like mebeverine 200 mg or hyoscine. for symptomatic relief with other water and electrolyte replacement.
If underlying cause is H pylori then you will require triple drug regimen means two antibiotics and PPI.
Consult physician or gastroenterologist for further advic.
Regards,