Maybe you can try to sort out the blocked nose issue first. If he has no appetite even eating cerelac or biscuits will be an issue.
When my baby had very severe blocked nose we tried these methods and it worked for us and improved baby's blocked nose.
1. Have a dehumidifier in the room
2. Before sleeping, bring baby into a hot steaming shower to ease nasal passage
3. Use Vicks Vaporub for infants to massage the chest and upper back as well as bottom of feet
4. If there is a lot of mucus, spray baby's nose with a nasal saline spray and suck it out using pigeon nose cleaner.
5. Lay baby down to sleep on an elevated surface using a wedge or tummy down (don't do this if you're afraid of SIDS)
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