Ryn I did a car trip at 32 weeks.
I know you won't know the destinations, but they and the hours in the car are as follows:
Home to Merimbula - 6 hours of driving time with half hour break after 3.
2 days later we drove from Merimbula to Albury via the mountains which took almost all bl**dy day with half hour for lunch and the odd leg stretch at a petrol station.
3 days later it was a 4 hour drive home from Albury.

We were transported in our lovely 1961 model holden so it wasn't the cushiest ride!

It is doable but I was stiff and sore for a few days after. Make sure you stop and stretch and go for a little stroll when you make the nescessary loo stops