I have just done my AS in both psychology and sociology, and I would say it was manageable. Psychology is a lot harder than sociology, but I did have a teacher in psychology who set 4 hours homework a night, no exaggeration.
In psychology it depends what exam board you are going to do, if its AQA
in the first year you will learn about attachment, memory, stress, abnormal behaviour, social influence and research methods. In attachment you will learn about how the types of attachment children make when they are younger affect their personalities today and how they handle future relationships. You will also learn the impact of children who were brought up in institutions and cases for example Genie who was in privation until the age of 13.
In memory you learn about how things are encoded, stored and remembered, there are two different models the working memory and the multi store model (you may want to research these beforehand), also learn about the impact of memory on eye witnesses and how social influence, expectations, filling in the blanks of a story will impact what they remembered.
Stress - you learn about how the body copes with stress, stress in the workplace and different personalities who are more or less likely to be stressed
Social influence - the pressure for people to conform to the group in order to be liked, fit in etc. and the pressure to obey authority - (this topic is very interesting with genius studies)
Abnormal - Here you will learn the different types of abnormality, therapies to help people with phobia's, depression, anxiety etc
Research methods - how studies are conducted, and how to criticize them
SOCIOLOGY AS
Here you will learn fewer topics than psychology and they tend to be a lot easier
you learn about the family, (types of family, how family has changed, feminists perspectives of the family, marxist's perspectives, functionalists perspectives, how the family can be harmful, marriage, divorce, )
also you will learn about the education system (teacher labelling students and the affect this has on their achievements, ethnicity and education, gender and education, social class and education,)
research methods (this topic overlaps psychology)
Hope that helped! But both are very interesting, my favourite is psychology