Respected Tapan, Hi I evaluated your query thoroughly.
*Clinically 
Gastritis with 
IBS induced decreased colonic motility.
*Continue medications as told by you along with lifestyle modifications for 
  better control of your symptoms.
@ Have plenty of liquids preferably boiled water, coconut water, home made
    juices, butter milk, rice water.
@ Take green leafy vegetables, cereals, legumes, high fiber diet, curd.
@ Avoid 
smoking / alcohol / abuse substances if any.
@ Avoid 
stress / 
anxiety.
@ Have adequate sound sleep of 8 hours.
@ Do regular Deep Breathing exercises with 
YOGA specifically Kapalbhati
    & Anulomvilom for 30 min. a day for long term life lasting results.
@ Avoid excess fasting / over eating.
@ Avoid excess oily / spicy / nonveg stuffs / beverages /excess ghee /sweets
@ Regular morning walking to get adequate fresh 
oxygen to rejuvenate 
    body , swimming , jogging other outdoor activities help.
@ Pre  & Probiotics, Amla for best herbal supportive help.
@ BE CONFIDENT all medicines are supportive only your inner wheel is 
    going to drive your life according to your desire.
  Hope this clears your query.
  Thanks for using Health Care Magic & reviewing my answer.
  Wishing you happy healthy life ahead.
  Regards.
  Bye Dear take care.