On Mastodon you can search just your own posts by including the phrase "from:me" in your search.
There are lots of these special phrases (called "operators") which let you customise your Mastodon search, so that you get a very specific set of search results.
You can see a complete list of Mastodon search operators in this guide:
➡️ fedi.tips/how-do-i-search-for-…
You can combine several operators in one search, or use a minus sign - before an operator to exclude it from the search.
How do I search for stuff on Mastodon? | Fedi.Tips – An Unofficial Guide to Mastodon and the Fediverse
An unofficial guide to using Mastodon and the Fediversefedi.tips