Aw, that sounds really painful, mama, a few of us went through something similar, and honestly the lump with pain can be mastitis or just engorgement, which really needs a doctor's check kasi it can get serious if left alone. In the meantime, warm compress before feeds and cold compress after helps some mums, plus make sure baby's latch is good on that side para ma-drain properly; if your left side is baby's favorite, try expressing a bit between feeds to ease the pressure, but best to see your OB or a lactation consultant soon para sure na okay ka lang at ma-rule out anything serious, yun ang peace of mind mo talaga.