Young adult with dehydration issues. Is this normal?

I am in my 20s, and even when I was younger I had issues with dehydration. When in the heat, I am extremely sensitive to it and become sick quickly. I always try to drink water, but I have been to the ER once when I had an “episode” and they said I was completely fine (other than my blood pressure and temp), I did some blood tests which were ok, and my urine was clear from drinking so much water. I am guessing my body has difficulty adjusting to the temp.

I work out in the heat and I can’t avoid it during that time as it’s my class time. Does anyone have any tips on how I can avoid being sick when we work out in class? I want to be there.