be sure to drink extra water, count the glasses if you have to.
the only thing that helped my plumbing was prune juice. I'd drink 1/2cup and wait 30 min before drinking another 1/2cup. If that didn't bring it on, I'd wait until the morning and see what happens and drink another 1/2cup if needed.
Metamucil bloated me up, stool softeners didn't help either. Seriously, prune juice was my new best friend.
The other thing I started doing was mark down the days I went. Other wise my memory was unreliable. On third day of no meaningful bathroom time, I'd reach for the prune juice. Besides, by day 4 I was starting to feel really bad.
and yeah, I'd say it's the progesterone, it relaxes the intestinal muscles. And oddly, the few times I got diarreah (sp?) it would give me hemroids. Go figure. (then witch hazel became my other new best friend)