Hello Dr.its Quite Urgent Please Help Sir. My Son Is

Hello Dr.its quite urgent please help sir.
My son is 3.5 years old (weight: 12 kg He has stomach pain for last 29 days.
24 hrs. he keep complaining about mild pain and every morning when he gets up and after having food he complains about strong pain and screems.
he don't pass the stool for 2-3 days and when he do he screems a lot in pain (2-3 hrs continuesly) and squizz his body and after that he feels good and when asked about the stomach pain he say No.
his stomach feels soft.
we had some tests too.
1:urine test: normal
2:T.B skin test: negatively
3:ultrasound/Sonography: "Gassy Bowel loops is seen"
on Doctor's advice we have stop Milk and spicy foods.
these are the medicines Dr. prescribed.-
1: cefixime oral suspension
2:Lansoprazole orally Disintegrating tablets
3:Magaldrate,Simethicone oral dilution
from 22 August:-
1: Duphalac Lactulose oral solution.
2:Amul kids (lactic acid bacillus 60 million viable spores tab)
3:Ranitidine oral solution
4:Sorbiline (solution of sorbitol and tricholine citrate)
nothing seems to work. still can't pass stool regularly. feeling so helpless please help sir.