I have no idea at all what Psychology is like, but I can absolutely assure you that Sociology is a total waste of time.
Honestly, it's more like a GCSE than an AS-Level; the exams are like 1 + 2 hours of regurgitating facts with no application or use of intelligence whatsoever. Especially if you've done it at GCSE, you'll probably just be reiterating the same old *******s. Seriously, go for anything other than Sociology.