swing needs help-low hook

Hey this is my first time on the boards but anyways I'm having some trouble with my swing. In spring I could hit roughly 200 everytime and I had a smooth easy swing. Now everytime I hit the ball it's a very low hook that sometimes barely even gets off the ground. I know that the clubface is closed at impact but I can't seem to fix it. Also, I have changed my swing a lot because I had the "good" swing in spring, then in the past few months to the recent change I would take a short backswing with a really powerful follow through which was a decent drive that went about 175 with roll. Every time I would do this I would hurt my back so I started to change my swing because of this. I've tried loosening my grip as well but that doesn't help either. I might be able to post a picture of the swing later. Thanks.