Hi,
Welcome to health care magic,
Stomach bloating is caused mainly because of air swallowing known as oerophagia.
The other causes are
irritable bowel syndrome or dyspepsia or
constipation or certain dietary habit changes which needs to be diagnosed by clinical examination and various investigations.
But it has nothing to with tamoxifen since it never causes gastric trouble or bloating or even a lower abdominal discomfort/pain.
You should start antacid medications like
pantoprazole 40 or
rabeprazole 20 with antacid gel like digene or sucralfate 2TSF two times daily.
Avoid excess carbohydrates and fatty foods,
Avoid oily and spicy foods.
Avoid cold drinks contains high sugar.
If you still have these problems then you should go for routine blood tests with ultrasound abdomen if had not done earlier.
Consult to physician gastroenterologist and ask for various investigations to treat underlying cause is symptoms persists.
Meanwhile,you may continue to take Tamoxifen as prescribed by your doctor.
Hope this helps.
Regards,