Anal questions please help

My boyfriend expressed to me that he would like to try anal if i was comfortable with it a while ago, so today I decided I guess I cant hurt to try so we did it for like 5 seconds till I sat up. it felt good and he liked it its just that so many people think its weird or nasty and I was one of those people that believed that was exit only. I kinda liked it im just torn between "thats a lil nasty" and "that felt really good" but also is it suppose to feel like you are shitting because that part was really weird? I didnt crap on him it just felt like I was about to, so was that just cuz I have never done it before or??