Had that- I found two remedies. 5 prunes a day (I found that they're easier to eat cold) and for "instant" gratification milk of magnesia... It took about 12 hours to work but it worked. After that, I have continued to eat prunes and I haven't had an issue since. Good luck
For extreme cases, a nurse at my OB last pregnancy recommended a drink of half prune juice, half milk of magnesia. Sounds gross but she guaranteed it. There are also some good suggestions in the hemorrhoid thread.
Re: Constipation?