Thanks, I am doing ok at the moment, hope you are too.
I am sure that the pool should be ok if it is at the ms society - the water should be between 21 - 25C for ms - too cold and we get stiff, too hot and our symptoms get worse.... You are probably doing too much because it feels so good! Try cutting backa little and see if it helps, also even though you are in the pool, you still get hot and sweaty if you over exert (you don't feel it though), which will raise your body temperature and make you exhausted, so gentle, slow exercise is best, not too much cardio, but rather more strength training.
My pool gets really hot in summer and if I swim during the heat of the day, I am exhausted after just a few minutes, and it takes me hours, even days to recover, so I stay in airconditioning, and swim at night.
I would imagine that it must feel great being out of the wheelchair - I am so glad that you have an activity that gives you joy, though I am sorry that this horrible disease has put you there.
Take care and experiment with cutting back a little.