Driver Side Door

I have a 02 Trailblazer. When I try to open my driver side door it sticks and is hard to open. If feels like I'm about to pull the handle off. Any idea what this could be?

When it is shut is it flush with everything else? When you get it open, grab a hold a the bottom of the door and pull up to see if it is loose and sagging. If it has a lot of play it might sitting akward with the door jam and making it stick. It might just need tighten up.