Hi Candy,
It seems to me you understand your position in any given situation and you act accordingly to how it should be if the authority figures weren't jackasses.
That's where things get complicated. When you need someone, such as your sister under present circumstances, you have to take a lot of crap because you don't have anywhere else to live. The problem is, she seems to know this and is abusing her position. You can either develop a big fat healthy dose of a sence of humor about her antics or you can stand up to her but be ready to have to move out in the event she'll kick you out. (Would she kick you out?) If she's use to you not standing up to her then even if you do so in the most constructive and right way-she's probably going to flip out.
With the doctor, I think you need to be more assertive because you're dealing with your physical health-why did he decide to switch you if your meds were working as was? Did you ask him?

(((((((Candybear)))))))))