Oh babe. You remind me so much of myself when i was 16, i was so fascinated with psychology at A level and then i studied at university which completely killed my enthusiasm for it. I too thought i would be up for a phd. How stupid i was!
My message to you is if youre really going to do this, make sure you know whats in the syllabus first because it barely resembles the stuff you do at A level. Personally i would choose something else.