I'm going to be honest with you, I've had the exact same fear and it's completely logical mainly because it's possibly true. Prior to my suicide attempt, I had asked my mother for help several times and she didn't believe me and she just blamed it on being a teen. But it helps to ask.Ask a friend.
Ask anyone.Reaching out helps and the thing is you can't bring it up subtly. You need to just tell them, no squandering.Hopefully it works out :) Im sorry if I couldn't be much help.
trust someone you believe will support you and stick by your side no matter what. they could be a family member/s or friend/s. try to tell it to someone you think will take you seriously, don't overthink it, and don't be ashamed or embarresed, it's normal.
I'd suggest telling someone you feel comfortable with as well (like your close friends or family members)! Tell them how you've been feeling lately and just try to let it all out and avoid sugarcoating it so they can see where you're coming from. I know it may be really hard to overcome the fears you may have with telling someone about this but you're trying to get the help and comfort you deserve and I think that's already commendable. :-) Maybe you could just start with a "Hey, I've been feeling a little different lately, can we talk about it?" and proceed with however you think would be the most comfortable way for you to go about telling them how you feel. :-)
Are you still in school? If so, your school should have counselors you can talk to about this kind of thing. I was in kind of a similar situation as you, I think. Growing up, I had a really unsupportive parent who would not get me help for my depression/other mental health stuff because he didn't believe in it. But I did have a really awesome best friend I was able to talk to about it and he's the one that encouraged me to seek professional help through my school and later in therapy.