Wow, I swear you are channeling my pain from 12 years ago, when I was 16.
It sounds to me like you have some depression fueling your need to smoke weed and cigarettes, drink, and eat junk food. Your story sounds just like mine, almost exactly... I was massively depressed. I thought I just wanted to lay in bed all day because I was lazy, and I hated myself for it. Nope, depression. I thought I liked smoking weed and drinking because it was fun. Nope, I liked it because I was literally miserable in my normal, not-high head space and any head change was a break from that.
Your parents are being awful, just like my parents were. I'm sure they're not trying to be, but what you said about your Dad cutting you out, and how your Mom is too busy trying to deal with her own crap... When you realize your parents' love might be conditional, when all you ever hear is that it isn't, that's fucking confusing.
So I was in your position, depressed AF, lowest self esteem possible, using anything I could basically to try to feel something better. My parents kinda kicked me out at 17 and I moved in with my online boyfriend and his family 300 miles away, and all of a sudden my life was 100% different. His parents were loving, supportive, forgiving, etc, TV parents basically. I went from getting C's, D's, and F's, to all A's my last year of high school. I didn't smoke weed and drink because I didn't want to disappoint them, and maybe because I was feeling better about me, too.
I tell you that last part because, when I was in your position I thought it was all my fault, but I think it was really a terrible combination of depression and severe lack of love and support. The adults around you are supposed to be helping you figure all this stuff out.
So the advice I want to give, after all that, is try talking with someone about your feelings, like the school counselor, or a teacher that you trust or even an older friend. It helps to be really in touch with your emotions, observe them an understand them, try to figure out where they come from. And, seriously look into getting your GED! My biggest regret is that I didn't just get my GED at 16 and GTFO even sooner. You could start college a year early, or community college, get a job, anything. Think about it!