A thick white discharge is a very common symptom with vaginal thrush. If you have any itching or irritation you should get yourself to the doctor.
If it's not got a foul odor, it's normal to have discharge at different parts of your cycle or all throughout that's different in consistency depending where in your cycle you are. It could also be that you got aroused at some point and the discharge got on your underwear.
If the discharge is cottage cheese in consistency, has a foul odor, or you have lots of itching, go to the doctor as you most likely have an infection.