Hello. I need some advice about some things I've been struggling with and I thought that this was the best place to go.

Little background info: I'm 18, I have anxiety and I'm currently in the screening process for ADHD. 

Over the last few days I've felt like utter shit. I started out just feeling a little miffed throughout the day at college on Monday, on Tuesday it got worse and yesterday I was temporarily kicked from college after having a meltdown and telling a member of staff that I couldn't go to my lesson over fears that I'd use something to hurt myself.

I haven't had a breakdown like that in a while, but a few months ago I did, and about two years ago I went through 4 or 5 months of being depressed but I never spoke to my parents or my doctor about it, only people from my old school.

My breakdowns happen every 3 months or so, I go through a phase of recalling all my childhood trauma and letting it influence everything I do in the present, and no matter what I do it looms over me like a dark cloud for a week or two.

I've realized that without the support of an adult at college I get super depressed super easily. I told college I was doing a little bit better and they basically dropped all support for me. The same thing happened those two years ago at my old school when the woman that I spoke to went on maternity leave and I was left with no one to really turn to. I emailed her a few times but then she got in trouble for it becuase we didn't know you weren't supposed to. When she let me know that we couldn't email anymore I had a major breakdown there and then and was depressed for days because she was the only person supporting me.

Currently I'm at home, off college and hopefully my doctor will give me a letter to give to my college tommorow to say that I'm fit to go back, as long as I have support. 

I don't know what this is but it seems to affect me quite a bit.

Any advice on what this is/what its caused by?

TLDR: I get really bad breakdowns every 3 months or so and can't cope without an adult (who isn't my parents) to talk to.