I'm doing two A levels and a 60 credit diploma. It is exhausting. All my subjects are really similar and there is a lot of content to learn.
I've known since year 9 that I wanted to do psychology at A level. Unfortunately, I never had the opportunity to do this at GCSE.
My sixth form course are A level Psychology, A level Sociology and diploma Criminology. It is no shock to me that psychology continues to be the subject I love and I'm incredibly passionate about it. However, it is also no surprise that I don't really like/enjoy sociology and criminology. But I had to choose three subjects so I had no choice but to pick two subjects to go with my favoured psychology. If it was up to me I would study psychology only.
My best advice would be to do what you enjoy most. You'll be more likely to learn. Also, do not overload yourself as your grades may fall.
Best of luck and have fun!