Stuck in a KonMari loop--need advice and help to break free

I've been following this subreddit after some time when I first read the KonMari book in 2015. I was really inspired by it and went through the process once, albeit a little rushed and not much decluttering occurred towards the end. It was just me and my sister living together in a townhome with a spare bedroom that helped keep the items I was going to throw away/donate/sell out of sight.

Fast-forward 2 years: family members from out of the country moved in with us last year and took up residence in that spare bedroom, so in a rush I had to get rid of all the remaining items in that room and place it in my room or find a "home" for it. I didn't realize I had so much miscellaneous items in that room and what resulted was clutter being shifted aside in a hurry. It was organized poorly in hallway closets and my room filled up junk again.

My room has been a perpetual mess since then and I've tried to undergo the KonMari process again but I always start off decluttering my clothes and end up coming short on the "papers/books" category. I get so overwhelmed and unhappy and then stop. I think I have some deep-seated mental issues here, but I really can't seem to declutter or even clean like a normal person.

I haven't been in a good mental space for a solid year and half. Life has been extremely difficult for me the since this year started. I have clutter everywhere in my room, clutter that has escaped my room to our downstairs living room in the hopes of finding a new "home" elsewhere in the house, mail and papers piling up--heck even my email inbox is piling up. Seeing everything cluttered and things that don't bring me joy stresses me out and lately my response to stress has been to sleep. I'm really trying and I hate to sound whiny, but I don't know where to start and I'm sick of going through my clothes for the nth time. Even starting off small somewhere ends up in things still getting cluttered by the end of a week.

Are there any tips on getting out of this rut so that I can declutter and really free up my mental space? What about items that you can't sell or donate but don't know how to dispose of properly?