I need to ask a question on a closed group, of which I am a member, but I don't see anywhere for me to post. The only posts I can see are from the admins. :/
It depends on the group settings. For instance, I am an admin of a group and I control who can post in it:
So unfortunately, you cannot do anything about it, if your group admin chooses to restrict posts by members.
Members of a closed FB group can comment on others' posts but CANNOT upload their own posts, despite the fact that (being the administrator) under "Story Posting Permissions" I checked "Αnyone in the group". What is the problem and how can I fix it?