This fact says you haven't finished the work in therapy yet, I'm afraid, as you're still suffering from your PTSD. I'm also wondering why you focus on fantasies as the only way to get turned on. Most of us get turned on because we like the person we're having sex with. I get the fantasies while you masturbate, but if you are fantasizing when you're with someone you like that usually only happens when you've been, ahem, married for a long time. (inside joke for those of us who are old married folks). But at bottom, what you're describing are lingering feelings from the horrible thing that happened to you. I wouldn't expect you to suddenly feel all of it is gone forever. I would expect it to be a process. And I would also expect you to benefit from more therapy so you won't feel bad about it being hard for you to move past it. But you will.
It won't be like this forever. I was raped at 20, and am much older than that now, but you need to give yourself some time.
If masturbation and sex brings back horrible memories, it just means you aren't ready, and maybe your therapy work isn't finished yet. That's okay - it doesn't mean you weren't successful in it. This is trauma, and it's tough stuff.
I don't want this to depress you, but this isn't something you "get over", but you get through. That means that it's never quite over. That's okay, too. I think it's important to know that, so that you can learn coping skills.
Give your therapist a call, or contact RAINN - https://www.rainn.org/
I swear it gets better, but give yourself some time and grace.