Anal??

Anybody have any tips on how to make anal “work”? I’m 19 years old and have only been able to do it once (well, several times, but it was one night) and that was with my ex when I was like 15. 🤦🏻‍♀️ The first time we tried that night, it felt alright. But we did it a few more times that night and each time after that, it hurt, like made my stomach hurt, and made me nauseous and I haven’t been able to do it since. My fiancé wants to do it so bad, I try, we’ve bought anal-eze, butt plugs, and nothing works. I can’t “loosen up” and calm down, it scares me because it hurts and I don’t particularly like it.. but i wanna give it a go, to fully succeed getting it in there so I know if it’s actually enjoyable to me now. Any tips would be appreciated.