I want to let you know that it is not uncommon at all for 4-year olds to begin exploring their sexuality. It is a normal part of human development. In fact, that is the age that most people have their first overtly sexual thoughts and feelings (beyond mere self-exploration and discovery), along with a feeling, based on training, habituation, and the mores surrounding us, that it is somehow "wrong".
Sexuality is hardwired into our brains and starts manifesting itself at around 4 years. Normally those feelings subside by about 7 only to be re-awoken during puberty. It does not mean you were abused when you were younger, and is not something to continue to be ashamed about.
I hope you find the understanding you are looking for, and that understanding somehow brings peace.