Make sure you stay hydrated and drink plenty of water!
I am going through the same thing! I have no ac at home and I work in a shop so no ac there. I am so hot ALL THE TIME! Sometimes I feel like it is hard to breathe. The only time I'm cool is the ride to and from work cuz the car has air. The summer is not fun while pregnant!
It's not good to be too hot, for too long. I would seriously look at getting a window AC, they aren't too much. At least have a fan on you and ice water. Sweating can cause you dehydration and be dangerous.
You cannot over heat. It is bad for the baby. Make sure that you stay hydrated and if possible either go to a friend/family members house during the hottest parts of the day or take cool baths. Talk to your doctor for extra advice.