If the changes happened with a food change, that would be my very first suspicion. Why did you change food? Can you change back? (Keep in mind that changing food, if it is the cause, will take a few weeks to show up - for the effects of the allergic cause to get out of her system).
You say it only happens after your evening walks? This also may mean that it's something in the air right now. Maybe google what's blooming or putting pollen in your air right now.
If it were me, I would quit that new food first and foremost. If, after about 3 weeks, I don't see any improvement, I'd take her to the vet for an allergy test.
__________________ Terri, proud mom to Mandie  & Shelby-Dale  |