Hi L. :O)
I read your responses, and I have tried all of them. They all work :O)
My oldest son needed a car ride, too, in order to relax enough to sleep. So, orginally, I just spread out and planned my daily errands so he would be in the car at the same time each day to (hopefully) fall asleep.
At your son's age, he can probably go a day without a nap, but then easily fall asleep the next day. This is what will begin to happen as he is outgowing his naps. Your routine will need to asccomodate his new routine. And, it will probably even be more interupted once your new baby comes.
Because you are SO pregnant, laying down with him is probably the best solution right now :o)
Just do what is easiest right now until you have that new baby, and then you can develop a new routine that works for all 3 of you :o)
Congratulations on your growing family!