Spellcheckers are great, but have several limitations. In most cases, if what it encounters is a real word, but in the wrong context, it won’t pick it up. For example, it’s a common typo to write “then” instead of “than” or “you” instead of “your” (one of my personal favorites). Since both are legitimate words, they’ll be missed.
If you know what your most common typos are, search on those words and make sure they’re used correctly. If you do this each day as you finish writing, you won’t be overwhelmed.