9 years old Labrador starting to pant and trouble breathing

I have a sweetheart of a Lab that is about 9 years old. Several weeks ago, she began to pant, and seem to have trouble breathing. She continually puts her nose up in the air and inhales sharply (wheezes) like she has something in her throat. It seems to come and go. On the first vet visit, she checked lungs, heart and gave her an allergy shot, it continued andon the second visit the vet partner gave her some Temaril, it does not seem to help, and she seems to be drooling some. Any ideas.’