You are saying it is occuring once in every 6 weeks but at each episode for how many days the fever is persisting and fever is associated with any joint swelling, rash , organomegaly
and lymphadenopahy and associated symptoms? These are to be looked into and depending on clinical examination and history investigations should be planned at different levels initially basic febrile profile investigations like CBP,ESR,MP,CUE, Widal test
, CRP,CUE,CXR and Mantoux test
and depending on these results next investigationls like collagen profile, bone marrow
and other serological investigations for infectious diseases depending on your child clinical profile and if your child is hemodynamically well except for fever he can be evaluated on OP basis so consult your Pediatrician
and infectious Disorder Specialist and plan accordingly.