Pls consult paedratican

How are you so sure that one side breast milk is bitter? A breast feeding baby can't speak so many words. When the baby is not accepting milk from one breast the first thing to do is to consult a Gynaecologist. Let him decide whether it is nipple problem or breast enlargement which is making breast tense and baby is finding it difficult to suck. It can be an infection of breast or nipple. Baby will accept milk after the mother has been given appropriate treatment.

Not possible

Any cracked nipple or discharge from the breast? Why would the milk from one breast have bitter taste.

Taste is same. There could be issues with nipple ( retracted nipple or inverted), due to which baby might not be able to suck. You can try silicon nipple shield.