feels like i'm not doing enough

I genuinely feel like I'm not doing enough revision for my GCSEs during this Easter break, while I did work really hard between December to Feb every day apart from weekends, and recently did my mocks as well in which I got decent grades but I can improve them. However, for some reason I'm struggling to concentrate + a family member of mine passed away too recently. I keep seeing my friends do more work than me and it makes me feel ashamed of myself as I should be doing the same especially as now we're only a month to go until the GCSEs. I've tried Pomodoro technique that worked for a bit but isn't working now and I've also made a list of tasks I need to get done before the exams. I don't know if I'm burnt out from all the studying but I can't even say that as I've already have had plenty of time to rest. Nothing seems to be going right.

Don't worry - I literally feel the same way...
I told myself that I gave myself a long break after Mocks, so therefore I should be effectively revising now before GCSEs. Yet I struggle with concentrating as well.
What I found out that works for me is by revising small - (e.g. today I do 30 min revision, tomorrow I do 1 hr, next week I do 2 everyday, etc...) and build up hours as a go along.
Moreover I believe there is a high chance you feel burnt out - but also confident you understand the majority of the topics from Mocks as well (So there's nothing to worry about!).
I would say go take a great rest day for now and get all your satisfaction - as your mind may feel fully confident in the topics you've done (resulting in revising less now).
I wish you all the best and good luck!

yeah its so difficult, how are you doing now?

Doing just fine (hopefully...!)
I'm doing my last bits of revision before I go back to boarding school - my first official GCSE exam is German-speaking on April 18. I'm pretty nervous as during my mock for Ger speaking, I was sick, and my voice died (no joke), so I couldn't concentrate + didn't do quite well.
I hope everything goes well though!
How is your revision going?

to be honest i feel like i haven't done enough, i genuinely feel like crying lol. if there's one thing i learnt from year 11 is how valuable time is in general