How do I know if I have depression ?

Hi I'm 17 year old girl and I have regular mood swings and my boyfriend of 11 months recently broke up with me and my nanas recently passed but even before these things happened I've been really down and I cry a lot over either nothing or things that are really stupid and I get angry at people. I've stopped eating too, and I just feel so lonely and I feel like my friends don't give a shit about how I'm feeling because they don't understand what's wrong with me, which also makes me feel down, like I just don't feel apart of anyone's life or feel useful, and no one really bothers with me. I don't want to tell my mam because she doesn't understand and it'd break out into an argument and I'm scared to go to the doctors because I feel stupid and my mam would need to know I just need something to make me happy and just understand because I actually can't really cope with how messed up my emotions actually are and have been for a while. Please help :(