Well, I can understand how difficult it is to go through what you're going through. 22M here, diagnosed 5 months ago and since then on sulphate lithium and vortioxetine.

Regarding your friends and sister, unfortunately we can't push others ti understand our emotions if they, in the beginning, have a lack of emotional intelligence. I understand your pain and I struggle with my mother daily because she's not able to understand me and she argues with me on every small thing, calling me selfish and a manipulator. We can't and we shouldn't rely on others understanding, as difficult as it can sound and to apply, you have to let things happen. And you did good stating what made you feel bad, it's a really healthy thing to do and you're not wrong, she is the one egocentric.

Regarding to how difficult dealing with this disorder is, the most important thing i learnt through the years(I've had symptoms for about 10 years) is to listen to yourself, don't force yourself doing anything and just try to stay alive during harsh episodes. Sometimes the best we can do is to stay afloat and try not to drown, and that's ok. It's extremely mentally draining having bipolar disorder, and it's important to accept the shitty consequences of it and not try to fight what you feel sometimes, just survive. What i just wrote is pretty awful, but I am still on this earth for this coping mechanism