I hate sex...

I don’t know if something is wrong with me or what. I never get turned on and when I do have sex with my fiancé, all I can think the whole time is I can’t wait for it to be over. I feel so guilty all the time because I absolutely love my fiancé but I just do not like sex anymore. We’ve been together almost 6 years and having sex for 5. I used to like it but idk what happened. Any advice? Thanks.