Is it normal to get really desperate for the loo during 4-hour shift?

Is there something wrong with me if I neeed to go to the loo every 3 hours? I lost my job as an admin assistant about 4 months ago, but managed to get a part-time job in a supermarket on checkouts. I do the evening shift 5 or 6 days a week. We sign on at 5.30 and the shop shuts at 9, but it’s nearer 20 past by the time the customers have gone and we can leave the checkout. I always find that by about 8.30 I’m ready to go to the loo, but I have to wait nearly an hour before I get the chance and by then I'm often busting. I’m used to being able to go when I need to. They say in training not to be afraid to ask for a loo break, and in the first 6 weeks I must of asked about 8 or 9 times, but most of the supervisors get a bit snotty about it, and they never in a hurry to find a replacement for you. Now I don’t even bother unless I’m in real trouble, cos I hate the embarrassment of having to ask in front of a queue of customers only to get tut-tutted at by a snotty superviser.

I've never thought of myself as having bladder trouble. At school I only ever asked to go once, and that when I was busting in a long exam, and I've only ever done it outdoors twice. I’ve never thought I’d have to go 4 hours without a loo break, and I can’t even cross my legs when I’m busting cos of those stupid stools we have to sit on. I just press my thighs together and lean forward a bit til the need dies down a bit. I’ve only seen 1 other person ask for a loo break since I’ve been working there, and that was just 1 occasion, though I did overhear another woman in the ladies saying she was almost wetting her knickers at the end of the shift.

So why do I find it hard to last 4 hours with out a break when everyone else is OK? Or do you just get used to it after a while? Sorry to bother you, but I’m on holiday at the moment and I’m not really looking forward to going back to work when I get home.