I am not a doctor, but is it possilbe that some how its related to oxygen levels?
Have you had a check up with your doctor, especially your cardiologist?
Could be allergies too. Not all allergic reactions are stuffy noses and watery eyes. Sometimes allergic reactions can be skin rash, sore throat, post nasal drip, etc. See your doctor....
tony, two questions:
Does the sore throat happen only during or after you work outside, or is it a problem most of the time?
2. Have you tried exercising indoors to make a comparison? The reason I ask is that if you can do something vigorous inside the house, like riding a stationary bike or dancing enough to sweat a little, and you do not lose your voice, then it might indicate that you were having an allergic problem with something in the yard.
But if exercise inside the house also causes voice loss, then you might be dealing with something else, perhaps related to blood pressure changes with exertion, for example.
I think you should definitely see a doctor for your mysterious symptoms--but it would be good to be able to tell him/her the results of the little experiment I mentioned above.