Dah 19 weeks macam tu memang common, sis, I punya friends dua tiga orang pun complain about back discomfort during pregnancy, especially kalau dah naik weight jugak. Tapi best lah you mention it to your gynae at the next checkup, sebab sometimes it's just ligaments stretching but better safe than sorry, especially kalau it's sharp pain or getting worse. In the meantime, try avoid lifting heavy things, make sure your posture okay, dan baring dengan proper support, I swear by maternity pillow, really helps dengan the aching at night. Take care!