It has happened to me a few times, even ruined one of the relationships I tried to have. To give you context, I was at a point in my life where I knew things happened, even though I thought had faced it, I had also just locked it away and hidden it so I wasn't really dealing with it.
Basically met this girl, we could be intimate remotely fine, like on the phone or texting. But then when we got in person, the most we could do with each other was oral and even that at times I didn't even feel comfortable doing it I felt like I was forcing myself so I would just feel normal. As soon as the idea of sex came up I would freak out on the inside and I could never figure out why, I ended up talking to a friend and he convinced me it wasn't what happened it was just that I was scared of getting her pregnant. I knew it wasn't that mainly because, if she did I would have settled with her happily, but there was just something there. I forced myself to try have sex with her a few times, even to the point she would get mad her friends were having sex and we weren't. I tried so many things even sex toys but I just couldn't get past the feeling not know what it was. Of Course she never knew what happened, I think I might have said something drunk once but I don't remember, and I know at times she seen I was uncomfortable and she would stop and just say we can do other things. To cut the long story short, she ended up going to a party getting drunk and sleeping with a guy because I she wasnt getting anything from me her words.
Of course this lead to a string of me forcing myself into uncomfortable situations after hearing a tony robbins talk, such as one night stands and tinder hookups, but every time I come away feeling terrible, where I would lock myself completely away from the world and just have an emotional crash without knowing why.
Its only years later to now, that I finally understand what happened when I was young and as a teenager, that I am finally starting to deal with things properly, that everything that was happening and making me feel that way was because what happened. becoming comfortable in myself, trying new things slowly trying to learn to become sociable and comfortable with sex of any type in general. I am using Hypnosis for this for allowing me to be more relaxed and comfortable with sexual topics and the social aspects of life, in general, it has been a big help for me.
Best Advice I can give...
Tell your partner that you have past trauma you are dealing with and that you need to take things slow with them, being afraid to tell someone to slow down still kind of terrifies me but it needs to be done.
And not to focus on it too much, it is related to your past trauma, it's not a physical issue, and it is something that with time and healing in yourself does start to get easier and more comfortable as you heal.