What Causes Stomach Pain And Gastroenteritis In A 5 Month Old?

Hi, I am koyel first time writing in hope of some help.... My baby (daughter) is 5months 12days old and is suffering from tremendous gas..she used to have it since her1.5months of age.. We used to give colicaid if required and her Dr. Suggested to give dimol drops for10days then.. But it never helped... It is very frustrating to see groaning in pain at night in her sleep.. Dr. Has suggested to start some apple puree, banana,boiled potatoes, lentil soup...and have tried apple puree for last 12days..otherwise she is exclusively breastfed. Please suggest how can I help her . also note for last couple of days she is fighting all her energy out to sleep..thanku..