I can relate to this, too, because I used to have the same problem in therapy, but have become... maybe not less introverted, but more willing to speak as I've gotten older.

When I was 19, I saw an analyst who wouldn't speak unless I did (and even then, not very much), so we spent over a year sitting in silence, my mind totally blank, until I finally fled the situation.

I didn't speak to the next therapist, either, and she got very frustrated with me, which lead to termination again.

With the therapist before my current one, I used to take in note cards with bullet points of things I wanted to talk about, or newspaper clippings or even comics that related to the way I was feeling and shared them with my T. He was very patient and open to this roundabout way of doing things. Gradually, I stopped needing props as my trust in myself and him grew stronger.

My current therapist is very emotive and chatty, so I have no problems talking to her at all, but this may be due to the groundwork laid by the previous therapist.

I guess the point of this is that, imo, your therapist needs to be a little flexible about working at your comfort level, letting you write at least some things down if that's what feels useful now, until you're ready to move on from there. Otherwise, you could just stay blocked and fearful.

Can you take a print out of your message to your next session? Just a thought.