I am sorry your dog Kopper is nasally congested. Since oral antihistamines haven't helped you can try pediatric phenylephrine as an over the counter remedy:
You would apply 1 drop to alternating nostrils every 12 hours for 3 days. It cannot be used longer than 3 days as it will cause worsening of the congestion past that point.
Please be advised that purely allergic sinusitis (allergy as a cause of nasal congestion) is relatively infrequent in young dogs and there may be an underlying viral and/or bacterial issue among other less common potential causes of this problem (i.e. nasal foreign body, fungal disease, nasal mites
If Kopper is coughing, lethargic or has decreased appetite, then I would recommend he see his veterinarian right away to make sure he doesn't require other more specific treatment. Likewise, if you try the pediatric phenylephrine and Kopper doesn't improve within 24 hours (despite feeling well otherwise), then it is likely that he needs to see a vet to figure out what is going on.
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