Common blockers: cheese, cottage cheese, rice, bananas, too much fiber, and sugar.
The standard looseners like prunes or magnesium don't seem to work for me. They just... TMI alert ... give me runs around what's already there, so to speak. It's like having diahrrea and constipation at the same time. For that reason, I'm afraid to try commercial laxatives.
Stuff that works for me:
Nuts and seeds. Not a wimpy ounce. A LOT, like a whole 6 oz jar of macadamias in a day. Or 6-8 ounces peanuts, or lots of sunflower seeds or pumpkin seeds. Seed meat only. Don't eat the tough pumpkin seed shells, those are sharp all the way through.
Tomato juice with cooked with fennel/anise. Again, use a lot. Like a tablespoon of fennel seeds for 2-3 cups of juice. Drink only one cup at a time until you know how it affects you.
Whole flax seeds. Eat a teaspoon 3 times a day for two days, then stop for a day, start up again. At least for me, flax tends to break up and soften. I get frequent urges of a little bit each time. It's very gentle on those sore muscles.
Good luck and sorry for the TMI!
5'0" female, 45 years old. Started Primal October 31, 2011, at a skinny fat 111.5 lbs. Low weight: 99.5 lb on a fast. Gained back to 115(!) on SAD chocolate, potato chips, and stress. Currently 111.