recalled abuse

I've had a vivid memory from when I was maybe 5 years old, of being in the bathroom with my dad. He is facing me, his penis is erect and really big. I remember every detail of what it looked like. I don't remember feeling scared or anything like that, just knew that it wasn't quite right. When I was a child I had a fascination with sex and the actual act of intercourse, which in my adult life I attributed to being from a culture where such things are no big deal. I have had a dream, which I can also recall vividly, where I'm a baby and my hands are on my dad's penis. I had this dream after talking with a friend about sexual abuse and whether or not it could have happened to me. As my body developed I was embarrassed to show it, and would wear a t-shirt at the beach, wouldn't let my family see me in my underwear, was paranoid that someone would walk in on me in the shower and locked the door whenever possible. My family teased me about this, my mother included, which made things even worse. No one in my family believes me when I tell them things that have happened in the past and my mother's favourite response to any vaguely dramatic story is that my imagination is running away with me.... I'm 37 and she still uses this tactic. To me, things point to some form of abuse, whether it is as simple as inappropriate sexual displays or whether it goes further I guess is just a matter of time. I know this has affected my current relationships and I know my behaviour is unusual because both my sisters, one younger and one older, do not have any of these odd types of behaviour. I'm having trouble believing myself that my dad may have done inappropriate things, but I guess that is what everyone has to deal with if they have been abused. What do you think?