I need to (not just want to) get better

I had been diagnosed with clinical depression 3.5 years back, and I had been suffering from it about a year earlier the diagnosis. I went to a therapist, didn't help much, i used to think that the therapist was incompetent but maybe it was the process, it was too long and I was impatient so I left therapy and tried to work it out on my own. I was quite busy and when I'm busy i try to remain busy, helps to get mind off things. Ok so my primary problem is the fact that I get depressed all of a sudden, without any apparent reason, and it happens in cycle usually toward tge end of the week like Saturday and Sunday, because I am home at these days. These days I only procrastinate, try to complete tasks that I had planned earlier in the week to do on holidays but fail miserably. These days my chest fills up with tears so much that even a slow melody or a quiet sunset makes me sob, I just can't help it as if I am some maniac, and whenever I try to find a reason for this behavior, it leads me nowhere. These two days I waste in this phase and at the end of these days i have cried and something suddenly changes within me and I start thinking that will be better tomorrow that I can do it, that life isn't so bad and the next day I am as cheerful as ever, so cheerful that if you ask a person that I see everyday at university they'll tell you that they've never seen me not smiling or laughing or making jokes. Usually these phases are short lasting a day or two, but when I am under pressure, they seem to lengthen like before an upcoming exam, and sometimes without a reason. And when these phases occur, it's like my immune system weekens and smaller problems or problems that I am not facing right now, thoughts about them start bothering me more than ever and i end up in a spiral that brings me down to that zero point from where I've climbed so much from. Why I am trying so hard to find a solution is the fact that I am a student of medicine and I can't help my patients if I'm myself one.