Oops you're right about the prune juice! (forgot to switch from maintenance brain to Phase 1 brain for a minute there!). But Psyllium husk and plenty of water should help all on its own.
Stool softeners like the Equate brand mentioned, or Miralax are also helpful. I've had constipation issues for years due to hypothyroidism, so I have a Miralax regimen that I go through about once a month.
If those don't get things moving, you can try a senna based bowel stimulant like Smooth Move tea - it works VERY well