Show number of posts next to page name

I created a page for each posts category, because i had to run a plugin inside a page. I call each category in each page (same name for cat/page) with a shortcode.
I have a menu containing these pages, and i want to show posts number next to each page name in menu. My question is how can i link each page with each category and which $var is that i need to put in the template? Thanx