Welcome to Healthcare magic.
If the discharge from your left breast is after childbirth it could be due to an patent milk duct which may be seen to discharge occasionally during hormonal
changes.In such case it is not necessarily bilateral.so your right breast may not show it.
But there are many other causes of discharge like nipple eczema
, infection , gland hypertrophy etc which need to be ruled out especially since the discharge is not always clear.
Kindly consult your gynaecologist for thorough examination and diagnosis.