Thanks for your query.
If you are not hypertensive and have no previous history of heart disease
then it is less likely that pain is arising from heart.
The symptoms you are referring are due to GERD
(gas) for that you are already taking antacid
You should avoid spicy food, caffeine, carbonated drinks and smoking
Do not go to bed right after taking meals.
Use extra pillows during sleep.
You may use H2 blockers or PPI along with antacid.
Take Vit B12 supplements and
You should check your Vitamin B12
blood levels as you are vegetarian.
You are advised to consult your doctor for further information
Hope it helps.