This is vaginal discharge. Discharge is normal and is there to keep you healthy. It can vary in colour from clear to white and can go from thin and watery to thick and gooey. It should have a bit of a smell but should not smell bad. If you have itching or stinging or your discharge is grey, green, frothy, smelly or thick, white and cheesy, see your GP. As a general rule, periods usually start 1 year after your breasts start to develop and discharge starts. You might like to wear a breathable liner if it bothers you on your undies.