Do I have some mental disorder? Depression?

Hey, I'm an 18 yo girl. I could tell u my life story, but I guess I will go straight to the problem. So last year after certain situations, which may or may not be the factors of why I feel and felt certain way I had a click in my head. Like smth switched and suddenly my constant mood became sad, meaning I woke up sad and I went to bed sad. Sometimes I had fun and laughed, but it wasn't for a long time. So that switch happened in August 2019 after a huge fight with dad, that ended up in me leaving the town back to my mom at literally 2 am)). I self harmed, but that was the only night I did. After that I had other events which couldn't allow me to rest. I distanced myself from others and sometimes would just cry. However I was still quite functional, I did all my school work (IB, those who knows will understand) and Im generally good at studying. I lost quite a lot of friends (almost all) and distanced from all. The thing is I deeply felt shit all the time. And in around middle of January I started feeling better. Again it was a click. Again maybe certain events caused the switch. After that I came back to my normal state, but now for around three month I started having similar feelings, but it comes for couple days, maybe a week and than goes. I try to fight it. I force myself into going out of bed and be productive,but it's extremely difficult. Again the thoughts come to my head that everything is pointless, etc. Aslo, I had a "fun" time when I was 13-15.5(after my parents divorced). I drank a lot, smoked cigs/weed and in general had a quite interesting lifestyle. (I'm so glad I wasn't offered harder drugs, back than I would say yes to everything). At this point i didn't drink for more than 2 and a half years, didn't smoke weed for more than a year and recently (hopefully finally) quite smoking, it's been 2 smth months. And now it's specifically hard for me, cuz I want to give up and go back to that lifestyle, but this time ik I'll do harder shit as well. Almost everyday I'm struggling and trying to stay sober and productive and not to go back to last year or years before, but it becomes harder. I don't know why this is so hard and if it's normal for ppl to feel it to this extent. So, recently I read thing abt depression and almost all symptoms were the same. I even did a quiz which siad I had mild to sever depression. But it sounds like I'm over exaggerating and as my therapist said it's okay to feel said some times. Although I didn't rly told her abt many things, still she is probably right. Or maybe she isn't, idk.. So my question is, if someone is a therapist or just been in a similar condition, what are your advices and or thought? Maybe you could tell me more abt this? Getting the same shitty feeling for such a small time, does it mean anything or again feeling said sometimes is okay? Any response would make a huge difference! (Also, sry English isn't my first language, so probs I had grammatical mistakes)