Hi ronzi, welcome and thanks for your question. Constipation isn't listed as a side effect of Evista, but since we all react differently to these meds, this just may be the way your body is responding to it.
Whenever I have this problem I increase my fiber rich foods and that usually takes care of the problem. There are also fiber tabs you can get at grocery/drug stores if you'd like to try those as well. If you can exercise, this will help too. Here's a link from the Mayo Clinic that gives a list of high fiber foods which should solve your problem.
Good luck. If you have any other questions don't hesitate to ask again.