I expect you lost it because yesterday you added it to an existing thread for another ID whereas today you started a separate one for it. You can keep track of threads you started by selecting the two little rectangular thingys beside your profile icon at the top left of the pages. For threads that you want to follow but didn't start, select "Watch" at the top of the thread under the forum name. I think I've got the latter right, someone correct me if I'm wrong.
