Mama, please contact your OB right away or go to the nearest hospital, yung severe belly pain while pregnant and on antibiotics needs to be checked immediately, hindi pwedeng antayan pa. Hindi ko magugustuhan kung pahilot-hilot lang kami dito habang buntis ka pa at may placenta previa. Your doctor needs to see you today, love. Could be the UTI, the medicine, the placenta previa, or something else entirely, kaya kailangan ng proper check-up, hindi home remedy. A few of us tried sa group namin na self-medicate while pregnant and it didn't end well, so please don't risk it. Keep safe!