Ay mama, I'd really suggest you get checked by your OB soon, UTI symptoms can be serious especially when you're pregnant, at 28 weeks pa lang kayo! Lower abdominal pain with nighttime bathroom trips definitely needs a proper check-up to be sure.
A few of my mum friends had similar concerns during pregnancy, at kinilala agad ng doctor kung ano talaga ang problema, kaya important talaga makita siya in person para ma-confirm. Gawin mo na lang itong priority, ha? Take care!