Concerns about my eating affecting my baby.

Recently, my daughter who is now 6 months old has been having problems with constipation. I introduced her to rice cereal a few weeks back and thought maybe that was the problem. Now with changing to barley cereal, than eliminating it all together and only giving her vegetables and fruit she continues to have this problem. I now think that it is my diet since she is nursing. I admit to not being the bet eater with also having a two year running around. Would anyone be able to direct to a book or website that can give me information on how to eat better while nursing? Or any suggestions in general to help relieve my little one of this pain and discomfort.

Thank You,