Should I rush to get an extenuating circumstanced form for Masters applications?

I have a decent 2:1 in my undergrad degree. But that's produced by a mixed bag of very high results and a couple of low 2:2s which have averaged out. I recently got rejected for my first choice course and they won't tell me why. So I'm wondering whether explaining my weird educational record might help.

I have a chronic physical illness which was recently diagnosed and was put down as a mental illness while I was studying. I had an individual learning plan (so that lecturers would know why I was absent / late with work sometimes).

In my second year I was really struggling with low energy and inability to concentrate and changed courses (from English Lit and French to French & Spanish, and I later took Chinese) as I thought the learning style would be easier to cope with (more technical skills and slightly less literary analysis). I had to wait until September for the next Spanish core module to start and I needed a break so dropped to part time for a year.

In my final year I got really physically sick and had to defer my January exams until the summer.

I got extensions on some essays and extra time in my final exams (I'd been offered it before then but never accepted).

There's even more to this including a complaints process due to an administrative error messing up my year abroad plans, a suicide attempt, and an abusive relationship with someone regularly having psychotic breaks and trying to kill themselves... . Which is why I kinda didn't want to get into it. I thought my grades turned out ok-ish and that would be enough but now I'm not sure.

One of my references mentions my illness as a reason for taking an extra year to complete.

Do you think it's worth trying to get a doctor's note in before the deadline for my next applications? I could maybe just mention the physical illness and leave it at that?