If you are having trouble keeping the water warm during a soak, you can try putting the container with the water and snake in his enclosure on his heat mat. You still need to monitor the soak at all times and take water temps, but it will help the water temperature stay higher longer. As Lord Sorril said, 3 weeks is pretty much nothing for a BP. However, you do need to monitor the snake's size and weight. A large weight loss is not good especially for a juvenile that doesn't have much weight to begin with, but 3 weeks, I wouldn't worry.