http://pets.thenest.com/severe-congestion-cats-7310.html
http://pets.webmd.com/cats/cat-nasal-discharge-nasal-infections
i would go back to the vet. the vet might be able to prescribe some further treatments.
http://www.aspca.org/pet-care/cat-care/herpes
sadly, the congestion and such are symptoms of the herpes.
What Is Feline Herpes?
Sneezing, congestion, watery eyes and nose.…Has your cat caught a cold? It could be feline herpes, also known as feline viral rhinopneumonitis (FVR), rhinotracheitis virus and feline herpesvirus type 1 (FHV-1), and one of the most common causes of upper respiratory infections in cats. Many cats are exposed to this virus at some point in their lives.
What Are the Symptoms of Feline Herpes?
Sneezing “attacks”
Discharge from the nose and eyes
Conjunctivitis or pink eye (inflammation of the eyelid)
Lesions in and around the eyes
Eye ulcers
Congestion
Fever
Depression
Loss of appetite
Drooling
Squinting
Lethargy
Once infected, the majority of cats do not get rid of the virus. However, symptoms can be treated. Veterinarians may prescribe oral antibiotics or antiviral medications to help ease symptoms, and drops or creams may be used for conjunctivitis or other eye irritations. With medication, good nutrition and tender loving care, most cats will make a successful recovery.
Please note, any cat developing an upper respiratory infection should be under veterinary supervision. A brief exam by a veterinarian will help to determine if your cat requires medication, has a fever or is dehydrated. If a cat is just sneezing, but is otherwise acting normally, no treatment will likely be needed. However, if a cat begins to show nasal discharge, loss or appetite or other symptoms, there is evidence of a secondary bacterial infection and cause for starting antibiotics.