I'm a bit late but 5 A Levels is, realistically speaking, impossible to manage. And make no mistake Psychology is still a heavy workload, there are dozens of experiments/studies you need to remember the whole procedure for and the psychologists who conducted them on top of all the processes, key terms, models, explanations, and other info related to research like the advantages and disadvantages of lab experiments. (as one small example)
Maths wont matter. If you're studying for medicine i'd go for Chemistry, Biology and Psychology. There are a lot of links in Psychology to medicine, such as treatments for depression, OCD and Schizophrenia if you chose the optional module etc.... I'm also doing ancient history for OCR and i love it, especially after the exam yesterday. It's a lot to revise but the exams aren't so heavy, they give you the option between two essays for each section so you can just write about the topic you feel more confident in. But if you're 100% sure you want to go into medicine then i'd go with Bio, Chem and Psych.