Help with doctor

i need time off of work and my doctor is only saying two weeks, even though i asked her and i told her i don't think that's going to be enough time, and she's not listening when i tell her im nervous to do PT because I don't want to get worse. i'm not diagnosed with me/cfs but am diagnosed with fnd. i don't think it explains my fatigue though. i feel trapped. i can't even work for an hour over an entire day in chunks bc i cant sit upright for more than a few minutes at a time without needing to lay down. and i can't even work while lying down. I feel so trapped and afraid. i was only able to work by using caffeine and energy drinks to force myself to get maybe a little more work done. i don't know how to make myself work. i tried to explain to her how bad it is but she says that i need to do PT. i dont know how to get someone to evaluate me for me/cfs so i can show what my limits are. i've been trying to keep up at work for months and years and i keep falling more behind and i have been so terrified of being found out. i spend almost all of my time in bed laying down even while working and i struggle to get anything done at all. i dont know what to do. my work has short term disability which i want to take but i need a doctors note.