I totally understand what you're going through. I am currently unemployed for the precise reasons you state in your post: unable to maintain focus, difficulty transitioning to new working environments, and then for me the social phobia and paranoia makes it nearly impossible to be "normal" in a work environment. I guess I would give it a month, three months ideally. If its really unbearable then I would quit. Putting a timeline on something usually makes it more bearable because you know quitting is always an option. If you liked the flower nursery, perhaps you should look for a position similar to that while you are working at the clothing store?