Forgive me for asking. How do you view your entire post history? I see the 'my posts' and 'my questions' button, but they only give results for any posts from the last 24 hours...

You can't.

Woah, that's a first. Ah well, thanks anyway. :)

And not the only one either.
Please vote for features you'd like to be added, and add wishes that have not yet been added. Here's one wish that's relevant to what you're asking for at the moment.

This way

As far as I'm aware the GOG forum software was hacked together by GOG using sticky-back plastic and bits of string. Perhaps they looked at their other options and found them too resource intensive or something? Doing everything yourself is not necessarily bad but it's a lot of work and maybe a bit more than GOG is really able to devote to it?

Anyway, if my mind is not terminally confused then I think they keep hinting at a big redesign for the website coming... sometime. Maybe the forum will get some love then?

or rather this way?

On the gog.com/forum page, right next to ' Topic I've participated in ' , there is a ' show more ' button. Unfortunately it is a bit wonky for some reason, but on a good day you can press it repeatedly to dig up very old posts. Today I could press it 3 times to reveal 3x5=15 additional threads I participated in (see attached pic). Some days I can only press it once before it disappears and on other days I've managed to press it 7 or more times. I sent a support ticket a couple of weeks ago regarding this issue of the 'show more' button not working correctly, and they said that they would look into it.

edit: http://www.gog.com/forum/general/topics_ive_participated_in/page1
^ Thread where I asked if anyone else also had an issue with the button

I view it with a touch of melancholy tinged with regret.

And fortunately there's an operator to filter out giveaways on Google :)

Ha ha!