Need advice on how to tell family about depression and self harm?

I have been feeling very low and very awful for the past year or so but I always brushed it away as stress. But in the past four months or so, I've taken a turn for the worst. My sleep schedule shifts from terrible insomnia to sleeping for 20 hours a day just to get out of the world for awhile and on the nights with the insomnia, I usually find myself scratching at my hands and thighs until they bleed because I want to feel something other than just empty or sad. Two nights ago it was especially bad because I came home from work after a fairly normal day and just started hitting myself for like 20 minutes. After that, I left really deep scratches on my legs. I feel really bad most days. Like, I can categorize my days into being sad, empty, or both. On the sad days, I can't move from bed much and I try to sleep a lot and I can't eat. The empty days are pretty much the same, but those are the days I usually self harm because I am upset at not feeling anything. Both days, I hate myself a lot and feel very self destructive. I keep a journal but it doesn't seem to provide any relief for these feelings. They never go away, even if I had a perfectly normal day. I live with my grandma and I am 17 but I am afraid to tell her because I don't think she will listen or understand and if she doesnt, I will have no hope of ever getting help. There was one night that she got upset with me and I locked myself in my room for three weeks and completely avoided talking to her. She thinks it's because I was mad, but really, I just used her frustration as an excuse for me to isolate myself because I was sick of pretending to be happy around her all the time. My hands are always marked with scars and open wounds and I've completely let go of myself and I'm failing my favorite class at school and I thought all of these things would be dead give aways that I haven't been doing well but she doesn't seem to notice and that makes me feel like she does notice but doesn't care. It has been a month and a week since her and I have been on good terms and I feel like there's no way she would ever take me seriously if I told her how badly I feel all the time. I want to go talk to my doctor because lately I've been wondering what would happen if I died. I'm not going to kill myself, but I think about dying all the time. Things like slowly starving to death or dying in my sleep. It terrifies me to have those thoughts, but most days and nights, I can't seem to turn the thoughts off or return to a state of normalcy. I'm afraid that if I get more and more depressed, I will eventually take it to the point of killing myself whether it's months from now or years. I talked to a trusted counselor at school a few weeks ago and he said to go to the doctor as soon as possible and a good friend talked to me on an especially bad night and asked if I had thought about taking myself to the hospital to get a mental health evaluation. I don't want to feel this way anymore and I don't want to seem crazy either. I just feel like I'm losing myself, like I'm always drowning, and I need to tell my grandma so I can get help.

does anyone have any advice on how to go about that? Or any stories of how they told loved ones? Thank you!!