It's more than possible that there was sexual abuse, since you've had this nightmare over and over. I couldn't imagine having that dream at 4 years old if something didn't happen to you, or you didn't witness anything sexual going on in front of you (which is sexual abuse anyway).

When I was a young child and some other kids would say things about sex, I felt like I had no idea what they were talking about. I also felt like I didn't understand the concept at all and I was sexually abused. It was really, because I didn't want to hear about it. Suppressed memories come from avoiding and dissociating. You would completely avoid the thought of the subject.

Intense psychotherapy and hypnosis can uncover memories we've suppressed. However, for me sometimes I just remember things when reminded of it like you explained, or it seems just out of the blue.

Anyway, you can post what your dream is about and use the trigger icon for your thread.