Thank you for your query.
I can understand your concern at the condition of your nephew. It is difficult to provide you with the causes of such a situation/condition, however, it is not uncommon for children to have complications following a bout of upper respiratory tract
infection. Though he may have received antibiotics but the organism need not be sensitive to it. A detailed workup, both clinical and investigative, will suggest the possible cause of such a condition. You are doing the right thing by getting him hospitalized where all the work-up shall be done.
I hope I have answered your query to your satisfaction.
Wishing your nephew an early recovery.