Uy mama, abdominal pain at frequent urination ay common sa 38 weeks, pero since you're this far along, please call your OB or go to the hospital agad para ma-check properly, mas safe na since they can monitor baby and make sure everything's okay.
A few of my mum friends had similar symptoms at this stage, and iba-iba ang reasons, basta hindi ka sure, better to get checked na lang. Wag mag-alala, the doctors see this all the time! Keep us posted, ha?