Aw mama, yan ang classic signs ng either plugged duct or yeast infection sa breast, at honestly kailangan mo ng checkup with a lactation consultant or your OB kasi mahirap i-diagnose lang based on description, lalo na kung masakit ang latching, one of my mum friends had the exact same "side lang" pain and turned out she had a clogged duct na kailangan ng proper positioning to clear. In the meantime, try warm compress before feeds, massage gently towards the nipple, and change nursing positions para ma-drain yung side na masakit, pero please get it checked soon because the longer you wait the mas prone ka sa mastitis which is a whole thing pa.