Go to your appt. if they fire you, so be it.
Consider working for yourself. It's liberating.
First, I assume they aren't paying your health ins. If not, then you aren't getting much in return for their draconian behavior.
Go to the library and check out the book, Guerrilla Marketing, and market yourself.
What are you good at doing? Cleaning? Then clean houses for a living.
Dog Sitting? Do you know how much kennels charge for a week? I'm paying someone $500 to come to my house once a day for 10 days while at I'm Disney to check on my animals. That's a bargain compared to the $1800 a kennel would charge for boarding.
Baby sitting? That prob requires some state credentialing but you can find out the details on the internet (at the library if no place else).
Find out what you can do, and market it at the right places.
Print a business card (cheap) and some flyers.
For example, dog sitting: see if vets that don't offer kenneling will let you leave cards or flyers. Check with travel agencies, etc.
Market yourself.
The closer you are to minimum wage, (and that describes being in a retail job less than a year), the more heft you can make picking a job you're good at doing, and marketing yourself.
You can, in fact, do both. Start marketing yourself now in your spare time, and when you "fill your pipeline" with new business and repeat customers, then quit your job.
Either way, an employer can't keep you from seeing your doctor. The only power they have over you is continued employment. For what they are paying you, you DO have other options at your disposal. Hold your head up high, don't take no for an answer, if they fire you, so be it.
You DO have other options. Take a hard look in the mirror. Trust me. You DO have other options. Believe in yourself, take care of yourself, and STAND UP for yourself.
Good luck.