Help!

I am 27 weeks and 6 days. I haven't worked my entire pregnancy, but I just started this part time cashier job at the mall. My very first day on the floor I worked a 5 hour shift. About 2 hours into my shift I suddenly got super hot and almost fainted, I had to sit down and drink some water. Then after that I started getting Braxton hicks contractions every 10 minutes until I got off. They didn't completely stop until I was back at home laying down. This has happened every single time I go to work, 2 hours into every shift. I go to the doctor Wednesday but I was wondering if any other mamas knows why I'm having this problem, or if they think it's normal or not? I also swell REALLY bad that i am having to wear a size 11 shoes when I normally wear size 8.