Yellow stains are more likely a sign that you should work on improving your hygiene by showering more often to wash away dead skin cells that end up on your undergarments. Additionally, you should make sure you launder your clothing between uses rather than wearing the same clothes every day without washing, which could lead to yellowing of white clothes in particular. Using chlorine bleach to wash your white clothes should help with this, as well.
The advice can't change from when you posted 3 days ago. See a therapist to try to get some relief from your fears, because no one on a chat line can provide that kind of one on one talk that might help you.