Thank you for your query.
i am afraid you are right. Costochondritis
doesn't causing vomiting
It is acid reflux
disease which is causing nausea and vomiting along with "chest pain".
Withold ibugesic. Give him omeprazozole and antacid solution.Avoid milk,fruit ,juices and wheat products.
For pain give buscopan
If you have any further queries you are free to consult me.
Hope this answers your query.
Wishing your child a speedy recovery.
Have a nice day