Unable to upload photos to new posts "unable to create directory"

I am using WordPress, with BlueHost as my host. I initially transferred my content from WordPress.com, but everything has been going smoothly with new posts. Recently, however, I have begun getting an error message that says “Unable to create directory wp-content/uploads/2014/01. Is its parent directory writable by the server?” when I try to upload photos to new posts. I am able to get around the problem by going to old posts, uploading photos and then inserting them in new posts through the media library, but I cannot upload to new posts or upload new themes, backgrounds, headers, etc. I believe it might have started happening at the beginning of the new year. Could someone walk me through how to remedy the problem?

Thank you!