Usually dogs with seasonal allergies have itchy skin and ear infections rather than coughing or sneezing.
You can read about allergies and dermatitis in dogs here http://www.lbah.com/allergy.htm It sounds like your dog might have either kennel cough
or canine influenza
If you think that is it then you can see if some Robitussin DM will help the dog breathe better and control any cough or sneezing or runny nose. Read here about cautions and dose info
If you see a colored discharge from nose or eyes, if your dog coughs stuff up, seems lethargic, has any real trouble with breathing, or goes off eating, see your vet as your pet may have a secondary bacterial infection that will need antibiotics or other meds.
This breed can also have problems with the trachea which you can read about here
Hope this helps you!