what do you do when people don't believe you?

I have bipolar type. I'd say I have a relatively mild case. I get really bad depressive episodes, but I can catch myself when I'm teetering on the edge of suicide and get myself to the hospital or otherwise get help. With my manic and psychotic episodes, they feel like hell but I pretty consistently have some sort of insight and I have yet to do anything life destroying. My sister is a psychiatrist and I guess because my case is more mild and she deals with a lot of more severe cases of bipolar/psychosis, when I talk about my mental health she will add in these little jabs that obviously imply that she does not really believe my diagnosis. It is to the point that, even though she is a very close person in my life, I am scared to tell her that I fear I am slipping into psychosis again. I don't really know what to do because I know I need help and really want to talk about it with someone but I am scared of her doubting me and possibly causing me to doubt my psychosis myself, making me believe the strange thoughts even more.