Early Christianity's a major topic of study for me, and for a very long time I was a Christian myself. What someone said about about early Christian's is entirely true; there was widespread teaching that people we do well to eschew sexual activity in order to best prepare themselves for the coming return of Christ. But this was not a strict rule and there was certainly no penance required of married couples who continued to have sex. But many married couples willingly chose to live as brother and sister in order to purify themselves further.
Early Christian documents such as the Epistle of Barnabas do show that sex for purposes other than reproduction were strictly forbidden, as of course they are by the modern Catholic and Orthodox Churches (early Christianity was a lot more like Catholicism/Orthodoxy than most evangelicals would like to admit). In fact even the Anglican Church forbade contraception until the 1930s, and the major Reformers also denounced it as evil...not a lot of people know that!
As has been said by a few people, mainstream Christianity has never taught that sex is inherently evil. This teaching was mostly put forward by the "gnostics", who believed that everything to do with the material worls was evil, and sex was included since it's a physical act. (I guess they'd never heard of tantric sex, lol.)