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The yellowish discharge from the vagina could sugest an infection. It could be bacterial, viral, protozoal or fungal infection. Most often it is a bacterial infection that causes yellowish discharge, be it from vagina or any other place.
Avoid douching the vagina, it alters the pH and make you more susceptible for infection.
Get yourself examined by your gynecologist along with testing the discharge to identify the infection causing agent. Get started on treatment as indicated by your test results. If you are sexually active get your partner also treated simultaneously and avoid having unprotected intercourse during the treatment to prevent chances of re-infection.
Take care.