What Causes White Discharge Before Periods?

Hi, Im 16 and ive been on my periods for just over a year. They only started getting regular a few months ago but in february i completely missed one when i went skiing and after that i started getting white crusty discharge and it was pretty itchy. Then i started getting creamy discharge but not that much. Then i started getting loads of discharge - really wet and horrible. This carried on until my next period started and everything seemed fine afterwards but now ive got the wet horrible discharge again and it has a really weird smell that i cant explain. Please help me!