Does your vitamin contain iron? If so maybe this is the problem and you need to try one that doesn't have iron in it. Check the list of ingredients on your vitamin container and if it contains iron then try a supplement without iron. Also if the vitamins are causing constipation they may not be the right brand/formula for you. You may need to try several different brands to find one that works well for you. Be sure they have a money back guarantee so you don't get stuck with a lot of vitamins that you can't use.