Your three year old is seen by you as someone else. You are very angry at this person, and project it onto your son. I would look carefully at the circumstance of his birth when you were nineteen, and your relationship to the father, or to the family or friends at that time that didn't support you, or pushed you into some corner you couldn't get out of. The fact that he is a boy, suggests that the person you are angry at is male......this is a good time to talk to a counselor and sort this out. It could change your whole life, and your relationship to your son.
I think if i have this right by reading this he looks like his father to much and you cant stand it just remember that he looks like you to. If im right i understand where you are coming from my oldest looks like his dad so much that he was hard to have him by me cause it reminded me what his father did to me and i looked at it like this its not his fault and never will be and he is apart of me and i stoped looking at him as his father