Constipation during pregnancy

I was told by the doc that I can take prune juice. It is very effective but cannot drink too much at once. If you have had constipation for a while, can drink 2 glasses a day. But once you start having soft stools, you have to reduce cause it will cause diarrhea when you take too much. Now I only take when I don’t poop for more than a day, and just take a small glass (about 250ml)