Metamucil can work well, but it has sugar or artificial sweeteners and colorings. I just use a pure psyllium fiber (which is the fiber in Metamucil). Konsyl brand is available at places like Walmart or online at drugstore.com. Also, you find many brands of this at Sprouts or Whole foods. Also, magnesium and vitamin C are both very helpful in this area and likely both things that will benefit you. Many, many people are deficient in magnesium and you can't take too much really - you'll know if you do because you'll get the opposite of constipation, which is why it works so well for that.
Also, you may already know but the last thing you want is to be constipated after childbirth - that was the worst part of childbirth for me. So, before I had my second I made sure to take Dulcolax