Due to some of my own excessive medical journal research in the past month or so it is possible there are findings but lack of findings on exam does not refute your memory and a medical expert for the defense could argue the point that the finding (if you did have such evidence on exam) is not always due to anal rape. That is what defense attorneys do.
I only know the system here, but we have child abuse assessment centers where the mental health and physical exam etc are completed together by professionals that do this routinely. That is the only place I would consider having this evaluated because I know that it was not typical for general medical training to get the finer points of sequelae of anal rape in kids. Plenty of pediatricians and GPs just don't realize how horrifically common this sh*t is, and unwittingly reinforce to the patient that it's all in their heads. I just want you to believe in what you know to be true, and recognize that medicine is imperfect.
Court and law are only one side of this, the other side is recovery and working through the inherent battle of PTSD to both remember and to forget the trauma.
Sharing this with someone you trust just to get it out is a good idea, you know your current providers. My advice above is more for the purpose of looking for proof of a historical assault on current physical exam-- medical experts in child abuse are more likely to know the subtle findings and be able to document them in such a way that they can be used in a court setting.
Good luck, I am sorry you've had to remember this, but for me knowing is so much better than not remembering. Just this year I remembered simultaneous vaginal/anal sexual assault by two family friends when I was between 6-8 yr old, and also recall having problems defecating around that time and also later noting a bulge around my anus and telling my mom, who did not take me to the Dr and then asked my grandma's physician during her visit about my symptom (so inappropriate) and then returned and told me it was fine, just a fissure. Now I know that was likely due to the rape, and fissures are not typical in kids (but are not a definite sign of abuse). So sorry that you've been hurt like this.