For me, I went all out in posting. Posting what could arguably be called too much. But its what I needed to do, for me. Get it all out to a shitload of people. Let the secerts go, to more then just my therapist because, with just him, it still felt like a secert. To me, this was telling "the world".
But, for you this may be fear of judgement, fear of letting "secerts" out, fear no would understand, possibly wanting to protect your abuser if a victim of abuse. That is something I still did in my first months here. Fear of anonymity. Fear of being "found out". It could be shame. It could be many things.
Maybe try to post something "small". A tiny bit of information, void of all details unneeded, asking a clear question or something clear to give advise on. Start small and I think, eventually, whatever the fear is will slowly disapate.
a) my question has already been at least somewhat answered someplace else
Those answers were for that poster and their set of circumstances, situations, trauma, mindframe. Your question can be completely different with completely different answers (and usually completely different posters replying).
b) whatever I was going to write about doesn't really matter and isn't good enough for the forum.
Everything and anything PTSD related (and issues caused by PTSD as well as the orgonal trauma(s)) is "good enough". There is no "good enough" standard here. As long as it somehow ties back to PTSD (since it is a PTSD board).
c) whatever I might say may be the wrong thing, and I may upset somebody else.
You don't have the power to upset someone. Not possible. They control their own feelings and emotions. They upset themselves.
I also don't like the idea of being searchable. I do realize that is how I found this place, so it isn't really fair to say that. At the same time, the thought scares me.
It scared me too at first and I did the very best I could to hide who I was, what State I live in, what other State I lived in, and even known phrases and names of things, known details, names I still don't say but my point is, I made myself as anonymous as possible because I have a family actively googling (and binging) me to find what sites I am on, they join (or just lurk), print out what they can, pass it around, gossip like mad, harass my dad about it and cause my life a living hell. They have yet to find me here and I have relaxed all the "can't say" things.
The chance of real world people finding you, even when searching for you, is nill and you can change your username once a year I believe. You can stay fully anonymous on here. I have.
I have not told anyone this site address. I do not follow the site's social media (so if they saw a snippet of my thread on social media, they won't know it is me) and those that live with me only know I am on "my site" or "the PTSD site" (they do not have the knowledge to google a forum for PTSD and do not know what a forum is - there are plenty of PTSD sites), and no one in the real world knows or could guess my user name.
Stay with that and you should be fine.