X-Ray was normal - this DECREASES the probability of it being a lower respiratory tract
infection like pneumonia
. The docs at ER must have also searched for murmurs
or other signs for endocarditis
and have found none - This was probably the reason why the ER ppl didn't ask for any more test. Trust the clinical skills, tests aren't always necessary !
However in view of the septal defect in your baby, I would advise you to meet some pediatrician
.Fever with no apparent cause, itself mandates further investigation but not necessarily emergency care.
Another thing , pain in chest doesn't always mean that that cause is some heart trouble so don't panic (panic wouldn't help anyway !). It can be because of some respiratory condition or even acid regurgitation disease (this' what I had thought of initially , but it can't explain the persistent fever).
So all u need to do is to take your baby to a doctor you believe in .Just tell the symptoms , show the X-ray film and inform of whatever happened at the ER.