I hope you don't mind if I laugh - it's so funny the way you tell it! (But not funny when you're going through it!)
My son had to poop in a plastic bag with paper towels in it, in the back seat floor of the minivan while I was driving on a turnpike that had NO WHERE to pull over. It was in 5:00 traffic. He had just turned 5 and he was in misery. My mom was in the passenger seat and helped him. It stank SO BAD, even with the bag tied shut, that we attached the bag to the passenger side view mirror and hung it outside the window, to give us some relief until we got off the turnpike and found a rest stop.
Honestly, sometimes I think that one day I will have to wear Depends to go on a long trip when I am old and gray, if I have to travel on turnpikes!!
Hope your little guy gets on a new schedule for you soon!
Dawn