Aw mama, that sharp, radiating pain from the side down to the bottom part of your breast sounds like it could be plugged ducts or mastitis brewing, lalo na if it's tender even when baby feeds, one of my mum friends had the same complaint at one month and it turned out she had inflammation sa tissue na yan. I'd really suggest checking with your OB or lactation consultant ASAP kasi ang sakit na yan hindi dapat i-ignore, especially if heavy pa ang dede mo at uncomfortable pa kahit lying down. In the meantime, try warm compresses before feeding, massage gently towards the nipple, and vary your baby's feeding position para ma-drain ang different parts, pero talaga, get it checked out soon para ma-rule out kung may infection na. You're still so fresh postpartum, mama, kaya kailangan mo ng expert eyes on this one!