To cite previous work, such as an essay you wrote for a different class:
An in-text citation for your previouly-written work would be formatted as follows:
If you referred to the work of others in your previous essay and mention that work in your new piece of writing, do not cite yourself for that source. Instead, include in-text citations and listings in your bibliography for the original source.
To cite a discussion post:
Note: the format of the citation would be the same if you were citing someone else's discussion post as well.
In-text citations where you paraphrase your own post would be formatted as follows:
If you directly quote your own words from a discussion post, you should give your reader a more information in the in-text citation. Include the paragraph number, if possible. (Yes, that does mean counting your paragraphs -- which could be considered a great reason for paraphrasing instead!)