I’m not meaning to. So what should i be doing?

Stop posting the same thing more than one single time.

How do i post across all communities and my blog?

When you post something it will go on your post feed and you can choose to "add to your blog". Whether you post in a community or not it's still a post on your post feed (everything posts to your post feed). You cannot post to all communities at the same time, only one.

Also why is posting more than once a day not recommended?

It makes it look like you are farming for rewards. My suggestion would be 7-10 posts a week, no more than 14 and no more than two a day or you'll attract the wrong sort of attention. There's no rule and you can do as you like because you have freedom...but remember that that same freedom extends to others.

I’m new and love writing about my day and my products.

See above.