Thank you for your question.
I am Dr. Su S. and I will try my best to help you.
From the history, it is likely due to a viral infection.
Tiredness, sleepiness are common in viral infection.
Viral infection usually subsides by 3-5 days, sometimes prolong though.
Only supportive measures are needed.
Please give plenty of fluid to keep good hydration.
Tylenol is good to control fever.
Ibuprofen can be given as well if Tylenol does not help.
However, if you feel he is having breathing difficulty, unable to take feeding, I would suggest to get her an examination by doctor.
Please keep the room humidified.
I hope this information will be helpful.
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Wish his healthy life.