I just started my Creighton classes! I will be married in August. I am learning a lot!
No it is not sinful to have intercourse during the time of menstruation.
**The Bible and Birth Control **is an excellent book for a foundation for talking with non-Catholics and does show Scriptural precedent regarding contraception. However, it is written by a Protestant minister. Therefore it has its limitations, and Sola Scriptura is one of them. This book seeks to argue soley from Scripture, and from some of the Protestant reformers’ interpretations of Scripture.
At any rate, Catholics recognize Scripture and Sacred Tradition. Therefore, the Church teaches that contraception is wrong not soley, nor even primarily, from Scripture. It is a violation of the Natural Law (built into our nature by God) and of the Sacrament of Marriage (and therefore the 6th Commandment).
Jesus elevated marraige to a Sacrament. Jesus built on the Jewish understanding of morals, as revealed in the 10 commandments, as well. He entrusted the teaching of the Faith to the Church. And, therefore it is the Church from whom we receive this teaching based on both Scripture and Tradition.
I recommend some solidly Catholic books such as **The Good News About Sex and Marriage **and Theology of the Body for Beginners, both by Christopher West. Also, the Catechism has a section on this and the encyclical Humanae Vitae is very instructive as well.