Regret taking people’s advice

You won't regret your decision for the rest of your life. In a few years time the A levels you took won't matter.
Drop chemistry and see if your school will let you swap biology for English. If not, do your best in biology, bearing in mind that a knowledge of the natural world is a useful accomplishment.
My daughter started the IB thinking of being a scientist, but changed her focus half way through and obtained a place at her dream university to study law. Your choice of A levels won't determine your path.

You won't regret your decision for the rest of your life. In a few years time the A levels you took won't matter.
Drop chemistry and see if your school will let you swap biology for English. If not, do your best in biology, bearing in mind that a knowledge of the natural world is a useful accomplishment.
My daughter started the IB thinking of being a scientist, but changed her focus half way through and obtained a place at her dream university to study law. Your choice of A levels won't determine your path.

I’m just really nervous really, i don’t want to look like a fool. I really tried to enjoy the sciences, I really did. I enjoy them at GCSE but…they’ve changed so much and I just don’t think they are for me anymore.

Definitely talk to your teachers about how you feel. It is so difficult to decide on just three or four A Levels and lots of students worry that they have made the wrong choice. It is sensible to take biology with chemistry if you want STEM options at uni, so it was good advice to take both - just unfortunate that you now know that your gut instinct was right and you want to study History. The excellent news is that your sixth form allowed you to start four A Levels so you have the flexibility to drop one (no-one really needs four, unless you are doing further maths and need it for uni). It is going to be a lot of work to start English at this stage, so listen to what your teachers say as they know your ability. One thing to consider is that if you switch to English, history and politics, you will have three essay subjects and your coursework load could be quite heavy (again, ask the teachers about that). If you stick with biology, politics and history, you would still have everything you need for your history degree, but you would also have one subject with a different style of learning and exam questions. Also, if you did start to look at other degrees, quite a few (e.g. psychology) ask for one science A Level. Having biology could help to keep your options open and, don't forget, choosing your degree is a bit of a journey through lower sixth. You might find you hate biology a lot less once you are down to three A Levels and are a lot less stressed. Anyway, the great news is that you have found the confidence to say that the current situation isn't working. If you haven't already, make sure that you send emails to all the relevant members of staff today (to ask about coursework) and don't delay even one more day if you end up switching to English. Sixth form can be an amazing experience, but it is a stepping stone. It is the hardest two years of your life and you might not have much of a social life if you are serious about your grades, but keep your eyes on the prize - you will have a fabulous time at uni (and only medical students have to work hard in first year 😉)

So, I’m not sure how I’m actually going to revise for it effectively. It’s would different if I liked the subjects and it didn’t make me ill. But, what’s the point of taking A-level bio as a third, when i don’t really like the content, and i can’t really use it to apply to most stem degrees (which I’ve already established I don’t want to do anyways). Plus, while I take your point about psychology, I’ll be honest I really don’t like psychology…I watched uni lectures on it before, and I found it kinda boring. Also, maybe it’s because I struggle with my mental health, but I found it triggering. I also have no interest in being a psychologist or anything like that, so i wouldn’t really see the point.

Plus, one of my concern with biology is that all the content on disease and cancer makes me really uncomfortable, like sick to my stomach uncomfortable. Ever since I did the cancer lesson, I keep freaking myself out thinking that I have cancer. So, it’s not that the content is not interesting, it’s just that it actually just freaks me the hell out. Like, I don’t wanna know the rate I have of getting breast cancer, i don’t want to think about that because otherwise I’ll just freak myself out.

It sounds like you may have generalised anxiety. Maybe talk to someone suitably skilled about that, or try mediation or exercise to assist with stress. A level essays should not be stressful, and if you are stressed out in sixth form you wont enjoy being an undergraduate, where the academic work is a big step up from sixth form.
The reality is that you will encounter cancer in your family or social circle at least once during your life, whether or not you get cancer. It's an unfortunate part of life, but science is advancing towards the elimination of cancer within the next century. The latest development is vaccines against some forms of cancer.

I know, I have talked with my my school counsellor about receiving support. I used to love school a lot more, and always wanted to go to uni, but now even though I still do, I just find it incredibly stressful and it’s difficult…I really want to go to uni, but I know I need some support to get to that point.