dear Mld, you can't carry on like this, it's wearing you down deeper.
You probably don't have to say much to the doctor they will be able to see that something is wrong with you, which in one way will be good, because then he will offer you a sick leave certificate for a month or so.
They are very astute as to how you feel, they have been doing it for a long time, and they will offer you to visit a psychologist which there are 10 free visits, please take this offer.
I would start to list details of your unpaid work, having to work week-ends, on your feet for 8 hours and all the other problems associated with the job.
It would appear as though you may have a case for discriminating against you or causing you to have this break down, so I would go and see a lawyer, no win no fee, and if by any means they sack you, then this just adds wood to the fire.
Because you have posted a comment on this site, means that you feel you are heading towards a breakdown, and asking for help.
If you can print your comment plus any replies back to you that would be even be better for the lawyer and maybe doctor and psychologist.
If you decide to do all or any of this, you need as much documented information as possible, that is the more the better, and this includes while you are on sick leave, and if you decide to take action, then let your psychologist know, that way they will document the conversions.
If your workplace hassles you on your sick leave, then let your lawyer put a stop to this, and please don't do it by yourself, because this will only make it worse for your condition. I really hope that this happens for you, and please let us know what is going on. Geoff.