Any suggestions to help with punctuation and spelling?

Rebecca, your written work doesn't exhibit signs of dyslexia; the mistakes you make are pretty much what anyone else makes before editing tidies things up. In fact, as I said about the story you put up for sharing, it was an astonishing piece of work for a 14 year-old; and it's still darn good after tweaking.

Everyone has difficulties seeing their own words. We hear what we intended to write, and overlay that onto what is actually on the page. There are ways to get round that: read it aloud; you'll trip over the words that differ, and the ones that are wrong.

Print it off in a different font and a different colour than you have used for writing; by changing its physical appearance, you will notice more.

If you do have problems with it after this, ask someone you trust - someone who reads a lot - to go over it for you with a red pen.

Does your computer have a grammar and spell-checker function? Make sure it's set to the English in which you write (UK not US, for instance). It will underline misspellings but not misused words, unless they are grammatically incorrect too.

Above all, don't despair - from what I've seen. you really aren't making huge errors.

As S.A Barlow writes, printing out your writing is a good way to spot mistakes.

I've also heard that changing the page colour and/or font colour can be helpful. Have you tried that?

Another idea that hasn't been raised yet is increasing your line spacing. I usually write in Word/Scrivener with 1.3~1.5 line spacing which makes for easy reading and writing.