I am wondering what kind of exercise you are doing? Intensity? How many days/hours per week?
Do you have fitness goals for your pregnancy?
For me, I exercise at a gym 5 days a week. I go in the mornings at 5:30 before work. I do 20 mins of body exercises or weight machines. Then 30 mins of treadmill walking at a quick pace going moderately uphill. Then, I end with 10 minutes of stretching.
I have one rest day usually Saturdays, and sundays I do yoga at a studio. Also, how hot is too hot for yoga? The yoga I do is not "hot yoga" but it does get pretty warm. I stay hydrated and lightly dressed.