i believe you and Im so sorry you weren't believed. Research has shown that your ability to recover from trauma like this hinges on whether you are supported and believed.
Why does it affect you now? Because trauma doesn't just go away. It hangs around and it hurts. Sexual abuse is one of the most destructive things anyone can do to another human being. And having lived through it, it's very hard, if not plain impossible, to go on to love in peace instead of in torment.
I find it sadly ironic that your sister is a social worker. Have you ever considered that, while she's claiming you had the perfect childhood, she's gone into social work to try to vicariously fix things by fixing other people's families?
People say stupid crap about victims being after the money as they're afraid to face up to the reality of how pervasive sexual abuse really is, they'd rather distance themselves from the reality, the repercussions and any idea that the victims are anything like them. People are often sympathetic for kids in newspapers but don't seem to grasp that wounded children grow into wounded adults.
You are not worthless. You were wounded in ways no human being ever should be. What you are experiencing right now is toxic shame - the belief that there is something fundamentally wrong with you. There's a poem about it called My Name is Toxic Shame, here's an extract:
"I came upon you when you were magical
Before you could know I was there
I severed your soul
I pierced you to the core
I brought you feelings of being flawed and defective
I brought you feelings of distrust, ugliness, stupidity, doubt
worthlessness, inferiority, and unworthiness
I made you feel different
I told you there was something wrong with you
I soiled your Godlikeness
MY NAME IS TOXIC SHAME"
I'm glad you are having counselling. That shame isn't yours and should never have been given to you. You deserve to heal.