This is normal. White discharge occurs throughout the month. When it turns clear that means you are ovulating.
When the white discharge reaches your underwear, it is exposed to air. This causes it to turn yellow.
At your age, you are not used to the smell of yourself. Often it can cause alarm. Every female has a slight odor down there, but it is healthy. Unless it smells from a far distance, it shouldn't be a concern.
What to watch out for:
If you start to smell a fishy odor coming from down there, you have an infection and need to go to your doctor.
If you start to itch or burn a lot down there and have a lot of discharge that is white and clumpy (like cottage cheese), then you have a yeast infection. Tell your parents so they can take you to a doctor. This is very common and should not be embarrassing.
If it hurts to pee, you pee and there is a little blood (not on your period), your pee is smelly, and you have to pee a lot through out the day, then you most likely have a urinary tract infection. This is extremely common as well and needs to be handled by the doctor or it can go to your kidneys and damage them permanently.
Probably a yeast infection. This is diagnosed and treated by a gynecologist.
To avoid yeast infections, use unscented Dove soap and wash gently every day. Dry thoroughly. Take a probiotic every day. Cut out sugary foods and starches, which turn to sugar and feed yeast. No sugary drinks at all. Eat more vegetables. Wash underclothes and towels and socks in warm to hot water with baking soda. Dry thoroughly after washing.
Usually yellowish-white discharge with a mild odor is normal, it just your vagina's way of cleaning itself out in between menstrual cycles. If you are itching, head into the doctor and get on some antibiotics because you might have a yeast infection (very common, don't stress too much about it)