Suggest Treatment For High Fever In A Child

My 3 yrs old son was started suffering with Heavy fever by Thursday 1st Oct 15 and doctor suggested only paracetamol syrup but fever was not even reducing then doctor suggested Syp.Mefanorm that controlled fever but dose was twice in day. Then I done Dengue antigen test after 36 hours on Saturday 3rd Oct 15, that was found negative but ulcers noticed in throat behind tongue. As dengue found negative, Doctor suggested to start Ibugesic plus to control fever, pls confirm is it fine ? however i have not started ibugesic plus but i am still managing with Paracetamol even stopped Mefonorm, doctor also prescribed multivitamin syrup that s dose is continued. Now Fever is not heavy and its getting reduce only with paracetamol but fever is coming 3-4 times in a day even after 4-5 days on Tuesday. Now my another Elder Son also started suffering with heavy fever and not being controlled by paracetamol only, so giving mefanorm syp also twice in a day and same condition that he also found ulcer in throat after 24 hours, also he is facing swelling on lips, now kindly help to know what kind of fever is to my both kids, is Dengue test required for my elder son too, both kids are not getting food/drinks,so how to manage, is dengue test required to younger son again? when fever will finish from both ? Thanking you in advance. Thanks & regards ..Rajneesh Parashar