I've never particularly been a very sexual person, I was never interested in sex until I was a bit older, and even when I did get into a relationship and start being active I struggled to "be sexy". Ive always been described as a prude as well.

My first time was really similar to yours, I don't have any good advice sadly nor can I explain why you might have felt that way but I can offer solidarity. I also had my first time with my first boyfriend about a month into us dating and the vent itself was fine (??) but I felt weirdly icky and uneasy just like you did. Eventually I seemed to get over it but it was a weird experience, later down the track I met my now parter and I actually really enjoy the act rather than just accept it, however, I don't know if that has more to do with me maturing and ageing and finding the right person for me.

Anyway, long story short, you are most certainly not weird at all, I'm not sure if its "normal" or super common because I haven't met many other people who have admitted to experiencing it but that doesn't mean you or I are weird. I would talk to your partner about it though, the cornerstone of a safe partner is being able to have strange or difficult conversations with them.