Help my kitty get care

My cat, Nelson, used to be 22 lbs but now I can feel his spine. Money is more than just tight -- I've only been surviving this year with help from others. I have an appointment at a low-cost vet but it's not until Nov. 30, and I feel I've waited long enough. I'm terrified it's something serious. Please, no lectures; I've had Nelson for 10 years, and this is the first time I've had neither money nor credit to properly care for him. My goal is based on what I've paid before for a battery of tests. If he needs treatment, I'll start another campaign. I don't want to spend my holidays putting down my mama's boy. :(