you should consult a pediatrician
as stomach ache with fever can be found in enteric fever
, UTI, gastroenteritis
, etc and also in cases of hepatitis.
or it can be just some viral illness with fever malaise and stomachache, that one can say only after examining the child.
nonetheless he has been ill on and off for past one and half month. so, it may be some chronic illness or infection your child may be having that needs to be evaluated.
for the time being you can give him paracetamol
for fever and body ache.