Hi Monny, Adam here in a very similar situation as your son.
Exactly as you describe, on average there is a week I am completely fine and out of a sudden (usually takes one or two days for complete switch) I am one week not able to function at all.
I am 29 and having this sine 20 yo, with minor fluctuations, but in general the state is still the same - good week following by bad one (sometimes 8,10 / 5 days, usually depression is longer)
I have been on probably almost every possible antidepressant; also on mood stabilizing medications for bipolar disorder and combinations with almost no effect at all (not even much of the side effects, maybe faster moods swing as you mention).
Currently I am on a new antidepressant which my doctor calls “last chance”. I am on another long term medication and I think it was the only one which – slightly - prolonged the “feeling good” episode.
I have also been on TMS (Transcranial magnetic stimulation), 2 rounds of about 10 sessions each. With not much of a recognizable effect ☹.
I am on a psychotherapy for about 2 years now. Not much of effect on the swings but helps sort things out. However, when depressed I find I pointless, we almost don’t talk at all. Thinking about hypnotization therapy.
As you mention – my psychiatrist finds this kind of cycling also strange; and haven’t found much info about it on the internet as well.
Do not want to make you worried, but me personally am very desperate. It is almost impossible to live like this.
At the time I have a good mood, I am grateful to be there, have lots of hobbies, enjoy life and still believe some new treatment will come (or me being “stronger” or “trying harder” or whatever). But honestly, I cannot imagine living like this for the next 10 years. I cannot imagine living like this for one more year.
Please how are you and your son? Any tips how are you dealing with it? Tell me you have some good news 😊. I pray both for you and me as well. With love, adam