There does seem to be rather a trend this winter for piggies having persistent URIs, our Blodwen has had a very bad run and is now being referred to a specialist.
As Wiebke says, if it is mostly nasal symptoms then irritants could be an issue, but also it seems this winter particularly many URI piggies are needing more than the usual week long course of antibiotics. Possibly a second course of the same antibiotic is needed, or switching to a different antibiotic- and perhaps the vet could take some swabs to see which antibiotic would work best, that would be quite easy to do with a nasal discharge.
If that doesnt solve things the next step might be xrays of the sinuses, teeth and chest- this might highlight either a congenital abnormality like a very narrow nasal passage, or something stuck in the nose or throat, or occasionally a dental issue can present with URI symptoms or even more rarely a heart issue- but that is less likely here I think as heart problems usually have more lower lung and less nasal symptoms, this is where we are heading with our Blodwen as her nose is always clear but there is something happening in her lungs.
So best get back to the vet, some piggies like some humans are just much more prone to respiratory issues than others, but hopefully this will be resolved with a longer course or different type of antibiotic x
