It sounds like you're quite happy working in retail at the moment. Do you know what your options would be if you took a year out working full time, and then decided you wanted to do a top up year later? Do you have any sort of long term goals?
You could consider working in retail for a while and trying to do some freelance photography at weekends. This would give you a bit more experience if you wanted to apply for a photography job in the future. If you already have a foundation degree, it's not like you have nothing to show for your hard work over the past couple of years. If you're not keen on the course, then doing it for a whole year might be a real struggle. On the other hand, if you really want a full BA, and you get the chance to transfer to photography, it might be worth it.
Good luck, whatever you decide.