*safe hugs* only if wanted...
I can relate to a lot of what you're saying, sister, and I know it's really hard when you feel so isolated.
I often feel (especially lately) like I'm not even really alive. I'm just watching life from behind glass. I feel so alienated from T, and everyone really. I have the same problem in therapy that you do... I sit there silent because I can't think of anything to say (or I ramble about nothing because I get uncomfortable with the silence). It drives T crazy lately.
Have you ever talked with your sister about your feeling of being on the "outside" when it came to the family? It sounds like your parents weren't probably very available to anyone. I'll bet your sister(s?) have experienced similar feelings. Maybe it would help you feel less alone if you knew they had?
I wish I had any sagely advice to offer. All I can say is I understand