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I would certainly believe that an ENT opinion is a good idea at this point of time,
Also I do feel that your suspicion that he may be trying to avoid school has some merits too,
Given the lack of any significant findings, the severe pain appears implausible,
Not many children with sinusitis have pain that does not respond to Lortab or tordal shots.
Certainly an ENT opinion would help clarifying this situation, and then further treatment including possible psychologist opinion can be considered,
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