TW for brief mention of suicidal thoughts/self harm urges 

So I've been tracking my mood for a couple of years now and noticed a pattern. I tend to have three severe depressive episodes a year , one jan-feb, one may-june and one oct-nov. During these episodes I struggle with intense daily suicidal thoughts, self harm urgesI feel very unmotivated, don't eat, sleep too much and basically barely function at all. Ive been on antidepressants for years and these never seemed to help. However, once the gruelling 7/8 weeks has passed I'm completely back to normal. I'm motivated again, my work drive is back, I'm inspired again and suicide doesn't even cross my mind for the duration of this period. In a way I even feel like I must be cured as I can't imagine feeling that depressed when I'm feeling so normal again and I even question if I was just faking it, which obviously I was not. 

From what I know its not environmental as I get these depressive episodes at the times I mentioned regardless of where I am or what season it is, like I could be on vacation and it would still be there. My psychiatrist has suggested that it's bpd which I disagree with as I'm completely symptom free for a couple of months at a time, and during my depression I only have 2 or 3 symptoms anyways. I guess I'm just wondering if anyone has any insight into why it seems to completely go away only to return just as bad as before, and in this pattern aswell, it seems unusual. Just looking to see if anyone has experienced anything similar. Thank you if you read all of this I hope you have a great day/night :)