I also had lots of trouble talking to therapst when I was younger. I started seeing therapist when I was 16. There were things I wanted to tell them, but I was too afraid and too ashamed. So I was mostly just answering their questions, but they didn't asked the right questions. It took me more than 5 years and lots of different therapist till I was finally able to open up about myself. That had also a lot to do with the terapist I got then. She was better than the others.
I don't know why you are in therapy. I started therapy because I had social anxiety and that was a huge part why I couldn't talk to therapist.

What's the reason you can't talk in therapy. Are you afraid or something? Maybe it helps to write things the things you would want to talk about down and then read it in therapy or give it to her?