I actually had my first incidence of BH's in the car today, driving for about 2 minutes then they started up.....Im well known for the amount of BH's I get late in pregnancy but have never had trouble driving before.
This lot of BH's has come along a lot earlier this time too....usually they kick in about the 34-35 week mark, now here I am at 30 wks and they've started up....usually when Ive been busy with my 3 y.o or with housework, they get going.
Ive found a good way to combat discomfort when driving is to move your seat forward but the back part of the seat back, so you arent all squished up, if that makes sense! I find that if the back part of the seat is further back than you would normally have it you are able to stretch out a wee bit more.