My Question Is My Baby Girl Is 4 And Half

My question is my baby girl is 4 and half yars old. She complains of serious irritations at her back and asks for continuous scratching for 10 minutes then she go to sleep . there is no rashes as such . why this scratchy skin there with my child .Another aspect is she often compains of stomuch ache . yes she used to suffer from constipation for long and now it has stabilized a little bit .Still it persists time and again . How this stomuch ache can be controlled otherwise she is asymptomatic.