First of all sex is not a sin. Unless the way you have might make it. If you think of that what you do is not according to the ethics of Orthodox church, yes it is going to be"Kedar"..... go a and tell everything for a Father of repentance('የንስሃ አባት') & will tell you what are the necessary steps before you can get baptized. You shouldn't get baptized before doing what he would told you........ probably it might be (ፆም ፣ ጸሎት ፣ ስግደት). You can go to church the next day after taking shower. Keeping your outern body clean, you then ask and prey for the inside