Hi Philipp,
I'm not a doc either, but I lived through pretty much what you're experiencing right now in the past more often than I could wish for. I went into major depression when I was about seventeen and had a breakdown when I was eighteen, and did see a doc then, who didn't prescribe me any drugs though. I felt better for a while, I guess mainly due to taking action, and since I still managed to get good results as far as grades went, I went studying, but these long periods of time when I was tired all the time stayed with me. I did what I had to do, but inside I was exhausted, with a foggy mind and not really knowing what I was doing, why I was doing it, and always waiting for those summer months where I could rest and then I'd need a few weeks still to feel a bit better, like I was getting in touch with myself, but before I knew it and much too soon the periods of rest would always be over and I'd be back in the grind. I was heavily addicted to daydreaming all the time, the one drug I'd always used, I could dream my days away, do nothing but lie there and daydream. It was the one thing I used to retain some inner emotional balance in a world that made no sense to me and where I felt helpless to do anything but to do and die.
And I did believe at times that it had to be something physical, cause though I was terribly unhappy at times, usually the ones where my mind was clear enough for me to realize that my life was nothing like the one I wanted to lead, at others my emotional state made no sense to me at all, and seemed not governed by my thoughts or experience, but to be like tides running through me. Like I could be incredibly happy about something one day, and I knew I'd be bound to feel miserable the next, as if I'd completely depleted some physical resource of mine. I felt good one day, and suddenly felt lousy the next two weeks to come with nothing happening outside to induce the weather change.
I've not been to a doc since all those years ago, but I've diagnosed myself with various mental disorders, the way you diagnose yourself with all sorts of emotional disorders once you start reading psychological books. In the end I find one is likely to jump on any solution presented regardless of its verification like grasping for a straw. I thought I had bipolar disorder myself for a while just a few months ago, but I read the symptoms on another site, and it wasn't really me after all. Also right now I don't believe the medical symptoms the ultimate answer anyhow, and the meds to be the solution. I simply don't believe that's the root of the experience, but that the real root from which the physical states stem lies deeper.
I don't know how much you believe in LoA or IM or how our emotions and state of being are indicators of our alignment with source, but I think there's some truth in that, though I don't know to what extent. But I do believe that depression comes not from some chemical imbalance in the body, but that the body shows the spiritual imbalance of the life experience and your soul. Meds might fix the symptoms, the red warning beacon that tells you you're off track and out of sync with who you really are, and that your energy level is really low. And they might help you to stay alive long enough to make the necessary changes, if you've ignored the warning beacon for too long, they might recharge your body for a while, but I don't believe swallowing a pill is the stand alone solution, meds alone don't make you change your life and fix the spiritual imbalance.
That's how I feel about it for my own person right now, but I am aware of the fact that a few people need meds their whole lives to be able to live a life worth living, and like with all things each one really has to decide for him or herself what applies to his own person, cause no one, not even a doc knows yourself as well as you do. And admittedly on a personal level I'm suspicious of AD meds at least, just as I'm suspicious of therapists for various reasons, and I have no way of knowing whether my thoughts and feelings are objectively valid, still they are to me. In the end you always need to do what feels in tune with yourself.
And finally I know how hard it is to look back and consider years of life presumably wasted, of not having acchieved what you wanted. I'm 32 and from the outside looking at my life, you'd say I was a pretty successful sort of person. From the inside a lot of times it feels I've acchieved far less than I could have, and wasted so many years away and that thought hurts. Forgiveness goes a long way for making your life easier if you can't bring yourself to believe that it was as it was meant to be. So when I can't believe that all was well and is well, and sometimes I lack that faith, I still know that I've been searching all the time, doing the best I was able to do being who I was at any given time. And that is exactly what you've been doing. So don't be hard on yourself, you probably wouldn't be lashing out like this at someone you love, so don't do it to yourself either. You're a seeker and you're gonna work things out in the end.