Should I choose sociology or History for A level

Hi! I am in year 11 right now and I decide to choose Maths and Psychology for two of my a level subjects. My dream job is to be a psychotherapist. I looked at the data and found out it's not easy to be a psychotherapist after graduating from university. (Of course I might be wrong) So I am thinking about being a social worker first and then be a psychotherapist after I gain the experience. So here is the problem: I really love history stories and I am interested in what I have learned in gcse history. However if I want to be a social worker I think sociology will help me more. I won't say I have no interest in sociology because I am concerned about what happened in the society as well. Again, thank you so much for reading! I will be glad if I can have some more information about it ^^

I really should write an article about picking subjects.

You don't always have to pick the subjects at GCSE/A Levels that you want a career in. The only way to know is to look at the job profiles for the career, and check the entry requirements for the degrees/apprenticeships if applicable.
Psychotherapist:
https://www.careerpilot.org.uk/job-sectors/medical/job-profile/psychotherapist
https://www.prospects.ac.uk/job-profiles/psychotherapist
https://nationalcareers.service.gov.uk/job-profiles/psychotherapist
Socail Worker:
https://www.prospects.ac.uk/job-profiles/social-worker
https://nationalcareers.service.gov.uk/job-profiles/social-worker
https://www.healthcareers.nhs.uk/explore-roles/wider-healthcare-team/roles-wider-healthcare-team/clinical-support-staff/social-worker
https://www.careerpilot.org.uk/job-sectors/childcare/job-profile/social-worker

I looked at the data and found out it's not easy to be a psychotherapist after graduating from university. (Of course I might be wrong)
No, that's pretty spot on. There's more qualified people with accredited psychotherapy degrees than there are jobs or work for them. Many go into self employment. As such, there is a lot of competition.
Having said that, there's strictly no requirement for you to have a degree to go into this line of work (see job profiles).

So I am thinking about being a social worker first and then be a psychotherapist after I gain the experience.
OK. Not entirely sure how this would affect your job application. You might want a second opinion from a qualified psychotherapist to check. From what I can tell, it tends to help if you did something related to psychotherapy prior to entering the field if you can't get your application through straight out of uni.

I really love history stories and I am interested in what I have learned in gcse history. However if I want to be a social worker I think sociology will help me more.
If you check the entry requirements for approved social work degrees (as well as approved psychotherapy degrees), there are no specific subjects at A Level that you need to take in order to do the degree i.e. you can pick something as random as French, Physics, and Philosophy and still get into these degrees. If the entry requirements of these approved degrees say something different, then please say because I haven't come across any. i.e. you can pick history, maths, and psychology (all pretty random anyway) and still get into psychotherapy and social work degrees.
Do note, maths and psychology tend not to be require subjects for psychotherapy and social work degrees.
Do also note sociology isn't a required subject, so you won't be asked to have studied sociology at A Level for any degree, unless you correct me. History on the other hand is a required subject for history degrees.
If for any random reason you feel compelled to study history or sociology after uni or college and take the exams as well (not sure why you need to), you can do as a private candidate. If you just want to read up on the material, you can do an online course or pick up the textbook for the subject.