How many applications are ok?

I feel like I keep trying to drive through a wall. I was checking on some of my applications today through the website of a local hospital and for all 10-15 jobs I had applied for I received the automatic response about them perusing other candidates yada yada. So I'm wondering if I am doing myself a disservice by applying to every job I see that doesn't require 3 plus years experience or some cert. that I do not posses. Should I limit my applications? And what is going to change if I keep applying with the same info. I have changed my resume and cover letter up a bit but it's all pretty much the same stuff.