I'm not a virgin but i'm scared of sex

I'm 20! I lost my virginity when I was 14 (I know that's young) but anyways I'v had plenty of sex before and well lately I'v developed a fear of having sex, I still have Sex but I'm nervous before and during it. I don't know why exactly but I sometimes think something bad will happen to my body if I have sex....I don't mean STD's or pregnancy....I mean something that causes injury.....is this normal, and if so does anyone know why?