Learn English – Using the words “post facto”

It's theoretically correct, you just need to add an article to make a noun out of the word post, like this:

I wanted to post a post, but I forgot to do so.

EDIT:

Either I didn't understand the question, or the others didn't understand my answer, so I'd like to rephrase myself: The above sentence is grammatical, there's nothing wrong with it from the technical point of view.

To go outside of what the OP asks, I would also add that repeating the same word is a bit unusual, but not incorrect. We don't know how the OP needs/wants to use the sentence, therefore we may not judge what's best for him.

To suggest some more usual options:

I wanted to submit a new post.
I wanted to create a new thread.
I wanted to add my reply.

The problem here is that there is not one true answer. Google will display the various styles used, but there is not one correct one.

To determine the style that you should should use, do the following.

Look up the word in the standard dictionary you are supposed to use. (If there isn't a standard dictionary for your project, choose one). If the word is in the dictionary, use that spelling. If not, look up the hyphenation rules in the style manual you are supposed to use. (If there isn't a standard style manual for your project, choose one). Hyphenate the word according to those rules.

For questions of capitalization, you'll have to refer once again to the style manual. It should contain rules for capitalizing hyphenated words. But be aware, the capitalization rule for a hyphenated word in a title may differ from that at the beginning of a sentence.

Example

Let's use your word, "co scheduling", and the rules from the Penn State Editorial Style Manual.

The manual specifies "Webster’s Collegiate Dictionary, current edition" for spelling and hyphenation. In that dictionary there is no entry for a word co that would properly modify scheduling, which means that "co scheduling" is incorrect. There are also no entries for either co-scheduling or coscheduling, so we can't follow the dictionary's spelling.

There are entries for the prefix co- and the word scheduling. So the word must be formed by merging these two. We need to use the style manual to determine how to do that. The section on hyphens states: "Words formed with the prefix co should be hyphenated." So if you follow Penn State's rules, the word should be co-scheduling.

The Penn State manual is silent on the rules for capitalizing hyphenated words and refers users to the Chicago Manual of Style in that case. That manual states: "Do not capitalize the second element if (a) it is a participle modifying the first element or (b) both elements constitute a single word." Because co- is a prefix, that means co-scheduling is a single word, and therefore the capitalized form is Co-scheduling.