Distracted while nursing

Has anyone else's baby become easily distracted while breastfeeding? My son just turned 4 months and recently has become SO distracted when I feed him. He latches and then pulls off at any noise or movement. I am beyond frustrated and worried that he isn't getting enough milk. I've tried different positions, nursing in a quiet room...I have to work very hard to get him to nurse for just 10 minutes and it has never been a problem like this before. Help :(