My Daughter Is 13 Yrs Old And She Has Frequent

My daughter is 13 yrs old and she has frequent excessive abdominal pain (around the centre of the stomach near n above the navel)this usually happens once in every 2-3 months .she has this unbearable pain for about 3-4 hours .during that time I give her decolic tablet .After 3-4 hours she fall asleep for about 2-3 hours . When gets up she feel better and I put her into very light diet after that for about 3-4 days ...
But this problem is recurrent in nature in every 2-3,month.What to do ????