Hi all,
I've read through the chain and everyone seems to be really helpful with this confusing matter. I hope someone will be able to shed some light regarding my situation as I've been really stressed.

Sorry in advance for the long post I hope I don't confuse you too much.
I applied for the UK citizenship on 17 April and was asked to provide CSI which is the first time I ever heard of it. I have 6 P60 forms from tax year 2021 to 2016. However, in tax year to 5 April 2016 I was a student and had 2 part time jobs - so I guess I was considered employed and CSI wouldn't apply for that time? I quit my job end of April 2016 as I had exams and then didn't have another job until October 2016 as I was in a process of graduating and finding a new job. However this counts as my qualifying period and I am panicking.
I came to UK in September 2013 as a student and had 2 EHIC cards each valid 1 year, however one of them is lost nowhere to be found and the other one says it expires 01/09/2017 so this means it was issued 01/09/2016. During second year of Uni I don't think I got issued a card (can't find it either) but I have paid health contributions in Bulgaria. Overall I have paid health contributions in Bulgaria until August 2016 which is my first month without contributions there. But then I got a job in October 2016 in UK, so I think I am only missing 1 or 2 months overall?
I saw people suggesting E104 forms as a proof that I have paid health contributions in another EU country at the time (Bulgaria) however when we asked how to obtain this form the health institution in Bulgaria they said they need a U1 form for the missing months from 10/2016 till now. I checked with HMRC and tried to submit a form to request this but you're only allowed this form once you're relocating and moving to another country

- can this be any more confusing?
Another thing I am a bit confused about is that they want me to upload 'Proof of living in the past 5 years' and 'Evidence that you have been in the UK lawfully for 5 years' - should 6 P60's apply for both?
Lastly I don't know, I think I got confused with the dates but I was out of the UK 4 times in 2016 and only added 1 of those times - how can I rectify this and give them the other 3 occasions? One is quite significant as well 39 days in Bulgaria 27/07/2016 - 04/09/2016 which links to my CSI problem above
I hope I am making some sense! Does anyone have any advise on this? Any help would be greatly appreciated, thank you!