your options are to quit or hang on.
it is retail so the work while not mentally taxing is hard. it involves much standing, walking etc. I would suggest investing in good innersoles...I know Walmart sells the dr scholls ones. try those. wear good socks with padding. protect your feet.

you know now there isn't going to be much training, but does your position really need it? instead of becoming so negative that it makes you ill, just focus on the positive. it is a paycheck. maybe not a great one, but it beats nothing. they are not asking you to design space shuttles but to just stock.

chances are if you chance jobs, the next one might not be enjoyable either. you have no way of knowing. entry level positions are just that. doing the most mundane level tasks. things that make companies keep rolling..nothing glamourous. it's good you liked greenhouses etc, and think that might be enjoyable but just remember that might not be an enjoyable career. I don't want to be negative but just want to make you aware...

I hated my first position in the area of my career. hated it. it took 2 or more positions within the same field before I truly fell in love with it. before that I was doing the most mundane tasks. could have quit but a paycheck is a paycheck. to your benefit, Walmart has benefits, my position did not. always rememeber in today's world that is HUGE. jobs don't define you, they are just a part of you.