Haha sis, yan talaga ang pregnancy hormones, super random! A few of us mums noticed na ang nipple sensitivity ay nag-come and go throughout pregnancy, especially around hormonal shifts, and kaya mo lang yan minsan triggered ng random things or even just friction sa bra. Mine were crazy sore in first trimester too, tapos second trimester parang mas naging manageable nalang pero still sensitive, kaya nag-switch ako ng softer bras at thankfully after birth lang talaga bumalik to normal.
Since you're noticing the soreness though, pagsiguruhin lang na comfortable ang bra mo and you're not chafing, if ever it gets really painful or you notice any changes sa appearance, definitely check with your OB, but honestly this sounds like normal pregnancy stuff na dadaan lang. Stay comfortable, mama!