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This white stuff is vaginal dischare, and its normal, just like there is saliva in mouth and tears in eyes.
During intercourse or sexual arousal , the quantity of discharge is increased, also right befor menses or during mid -cycle its is seen .
Its nothing to be scared of, untill it changes its color, has bad odor, or cauese itching/irritation
P.S - Using condom is not a bad idea.