I drink a lot of water and I usually sweat profusely after 10-15 min of exercise, however I've noticed in the past week I've felt thirsty and I've been drinking water, but I'm not sweating. I might start to perspire after 45 minutes of exercise and that is just not like me. And it's a light sweat when I do. None on my forehead and I typically pour sweat from my head. I also have had a burning sensation in my stomach. This started 5 days ago. To the point where I had to drink pepto bismal for two days to relieve the feeling. Those are two very odd things to start around the same time, but I'm a very healthy person, still extremely athletic at the age of 43.