Write it down...writing has helped me so much get through the hard to talk stage. I think it would be great if you could say to your T - I'm scared of being vulnerable, but just in case write it on a piece of paper so you can get the thought out.
I think we all get stuck in therapy at different times for different reasons. Being stuck doesn't mean that it needs to stop, it just means you need to try to figure out what is making you feel stuck IMO.

I have also found regarding anxiety that the thoughts before the event are so much worse than the event itself. What is the worst thing that could happen if you went to the doctor? If you can identify what you are afraid of, it might be easier to conquer.

In terms of the over-thinking things, I do that also - very often, my rational mind tells me one thing but everything inside me is fighting anything rational. I've tried to step outside myself and consider what I would tell a friend if they were experiencing the situation I was struggling with. Sometimes that helps you look at things from the outside in, rather than from the inside out.

Hope this makes sense!