doing an entire humanity a level in one year? (as a private candidate)

(context: currently in y12 doing 3 a levels but i rlly hate one of them and want to drop it/will probably get kicked off the course after AS exams)
can i privately sit an entire a level (humanity) subject in year 13 alongside my other 2 a levels that i'm doing in sixth form? is it too much content to get done in one year or is it manageable with enough effort? also, how do i go about getting a predicted grade if i'm self studying it? do i need to get a tutor or should i just take a gap year after sixth form and apply with my achieved grades? any advice about sitting a level exams as a private candidate would be really helpful as i'm not really sure where to start looking.
extra question: do exam boards matter? im in wales so all of my exam boards are WJEC, but if i privately sit an a level i want to do AQA as there are more resources online to help me

(context: currently in y12 doing 3 a levels but i rlly hate one of them and want to drop it/will probably get kicked off the course after AS exams)

can i privately sit an entire a level (humanity) subject in year 13 alongside my other 2 a levels that i'm doing in sixth form? is it too much content to get done in one year or is it manageable with enough effort? also, how do i go about getting a predicted grade if i'm self studying it? do i need to get a tutor or should i just take a gap year after sixth form and apply with my achieved grades? any advice about sitting a level exams as a private candidate would be really helpful as i'm not really sure where to start looking.

extra question: do exam boards matter? im in wales so all of my exam boards are WJEC, but if i privately sit an a level i want to do AQA as there are more resources online to help me

Unfortunately, the best bet would just be to firm the situation you are in and continue with your 3 A levels. You've only got one more year left of this. As much as it sucks, you have a much much better chance of achieving a decent grade in your 3rd subject (which you hate) than a new A level if you were to pick it up now, especially with self studying.
Sitting exams privately is also expensive. Y13 is a lot harder and more intense than Y12. Keep in mind you also don't have the whole year. You have until April at best. A level exams usually start in May.
Is the new A level required for a course you want to study at uni? You mentioned that it's a humanities and many (if not most) humanities don't have subject requirements. Grind through your 3 for one more year and study something you like at uni. It will build good resilience and teach you a lot.
[I took further maths and maths A level despite maths being my least favourite GCSE subject - I spent the entirety of Y12 self-studying other A levels and wishing I could drop maths. Ended up dropping my self-studied ones at the end of Y12 and just accepting my fate. I'm going to study a humanities course at degree in October and maths has taught me a lot of good skills, no matter how much I hated it at the time].

the subject i want to drop is chemistry so it's definitely not required for any of the courses im interested in, honestly don't even know why i picked it. i'm going to try and do well in my AS exams this year because privately sitting another a level is expensive and i want to avoid it as much as possible, but it might be my last resort if i fail the exams so idk.

I meant what A level do you want to study instead?
(Completely understand the chemistry hate btw - oof)

probably sociology because i did it at gcse and enjoyed it, so i know i'll enjoy the a level content too. also it has loads of resources online, especially for aqa, so i should be alright learning most of it on my own