If you are fortunate enough to be in an area with employment options then I would echo the previous recommendations to look for something else
but do not quit this current job until you have definitely got something new to go to. Anything where you have to meet the public head-on is going to be stressful because you will always be the first person they vent to/complain about/abuse/stalk.
Restaurant work can be insanely busy, rewarding and sometimes stressful if you get fussy customers coming in - but if you're allowed to earn tips that you don't have to share out then you can make quite a good bit of dough, meet interesting people and work better hours. Plus there's usually some sort of discount involved and a meal provided if the hours are a little unsociable.
Working in a shop depends on the size of the store and what they are selling - check out the reputation of the shop you want to apply for because sometimes it can be a place where its known for shoddy goods, poor customer care, looooooong lines of people returning stuff that has obviously been well-used for the past 3 months yet they are throwing bits of their Statutory Rights at you to intimidate you into handing over the contents of the till as compensation...you get the idea. Small stores can mean long hours of doing crap-all, busy stores can mean long hours of monotony - it depends on the job position, the company and the people you are with.
Avoid the hotel and leisure industry like the plague unless you actually enjoy abuse on a daily basis. And unless you are into the whole competitive scene, don't get a job that will insist upon you achieving targets to earn above-the-breadline-style wages. Bar work can be incredibly fun and offers quite a bit of money too - pick the right pub/bar and you're laughing.
If you can handle it and the hours fit (and you keep it above board with Mr. Inland Revenue), get a couple of part time jobs that are different to each other and see which area you prefer. Also, ask around mates and their families to see if anyone knows of anything going begging work-wise. Sometimes knowing someone who can get you an interview or probationary period working elsewhere can be handy.
And if you're stuck in your current job for the foreseeable? Keep trying to set yourself those personal targets, no matter how small or arbitrary they may be. Make sure the days/times you're not working involve you having a good time, doing the things you enjoy, being with the people you like and no talking about how crappy your job is. Off the clock means just that
P.S. If you happen to ever call our house and I answer, apologies in advance for how unbelievably rude I will be to you. Nothing personal.