Anal tips?

Let my boyfriend get it in this morning...well he tried.

At first I didn’t mind it but the more he fingered me and the more I sat there and thought about it the more I grew uncomfortable(how it feels like I’m constantly pooping or I’m going to shit even though there’s nothing in there).

He barely got the tip in and I was already in pain. I really want to try it because I know my boyfriend enjoys it and I want to at least experience it once-but how the hell do I get passed the pain of it all because I am the biggest baby ever!!!!!!!