Golden Retriever-coughing (gagging) and sneexing

Hello:
Before i go to the vet i was hoping I could get some over the counter assistance. 6yr. old goldren retriever is coughing almost gagging like he wants to vomit,but not able to.
He has been sneezing on and off-allergies?
He is also limping a bit and I have been giving him glucosimine for the limp, but yesterday discover he will pull his front paw away when I push on his pad.
He doesn't appear to have cut it?
Please help-thanks

Coughing and sneezing is more likely to be kennel cough or another respiratory infection. Dogs rarely (if ever at all) get sinus allergies like humans do. Allergies usually manifest as itchiness, ear infections, etc.

The limp is definitely something the vet has to look at.