Humanae Vitae is one of the most important encyclicals to read in this regard. Had everyone listened up when it was written (me included!), there would be less abortion in this world, and more love between husband and wife. http://www.vatican.va/holy_father/paul_vi/encyclicals/documents/hf_p-vi_enc_25071968_humanae-vitae_en.html
I am not a Catholic and do not subscribe to the Catholic ideal of refraining from physical interactions except for the purpose of getting pregnant. That whole ideal is unrealistic because it does not take into account the very strong biological imperative to engage in physical relations frequently (even during pregnancy). If a married couple wants to limit the number of children they have—few people can afford unlimited children—then, realistically, they must use some form of contraceptive to achieve that limit.