I have heard a lot about soy. But it isn't a magic bullet.
There can be more than one possible cause of your symptoms. It doesn't have to be menopause.
If I were in your shoes, I would find a physician that can communicate with your usual doctor from home. Just to be sure something mysterious isn't going on.
I am not so sure it is hot flashes when it is induced by exercise. It might just be de-conditioning. Is your pulse doing what it should? Take it before, during and after exercise until your symptoms subside. This information would help a doctor, and tell you a little more as to whether you need a doctor.
If you don't know how to take your pulse, use the info in this article. www.sparkpeople.com/resource/fitness_artic