It may have allergies'. If you have started using any new products like cleaners, or soaps and shampoos even for yourself stop and see if that helps. Try giving an allergy medicine containing Diphenhydramine, 1mg per pound. If that doesn't work you will need find the money and take them to a vet
It can be allergies or an infection. If it's a hound dog with droopy eyes, there's also a condition where the eyes are inflamed. You need to take the dog to the vet to be examined, as any of these issues can get serious very quickly.