I went when I was 7 months pregnant. We went at the end of August into the first week of September. It was extremely hot and humid. My doctor said to keep a bottle of water in my hand and DRINK, DRINK, DRINK!!! We have gone many times, so we took this opportunity to enjoy our last few months as a couple. Enjoy air-conditioned restaurants and the pool. I found that swimming or floating in the pool was the best! Take your time and when your body tells you to stop, STOP! One night, we had to take a taxi from Beaches-n-Creme to POR b/c I just couldn't walk through Epcot to the buses. It was worth the $$. As long as you are feeling good and your doctor says it is okay, go for it.
As far as the Safari ride at AK, I went on it b/c I had been on it before and knew how bumpy it would be. But, there are warnings for pregnant women to avoid the ride.