Dizzy in car

So this has now happened to me 3 times. I go to work for 4pm so I spend most of my day inside as it is hot out and I am 31 weeks pregnant. On my way to work I have been getting dizzy (I don't drive). Just sitting in the car I get nauseous, start sweating & everything gets super bright to the point where I can't see. Once the car stops I calm down but I don't know why it's happening. One of the times I even fainted / blacked out and hubby pulled the car over and had to wake me up 😁 I asked my dr about it the day after and she thinks it was just a rise and drop on my sugar levels. It happened again the next day but not as extreme. It only happened once before that too but again not as bad. Just the sweating / brightness. Anyone experiencing something similar or know what could be causing this? I have to work today and I'm nervous about getting in the car & feeling sick. (The AC was on all these times too if that matters.. Fresh air usually helps some once I feel sick)