Ask your Ob doctor
Use of hot tubs while pregnant is controversial.
One should realize that it is not unusual for your temperature to increase quickly when you are in a hot tub because often your entire body is immersed in a hot tub, but in a bath tub only part of your body is in the tub. Also, water in a hot tub is heated while you are in the tub. One should definitely talk to the doctor before using the hot tub.