Wa'alaikumassalam! Normal je tu sis, especially around 13 weeks, uterus kau tengah berkembang pesat so rasa macam senggugut atau cramping tu common. Tapi since you've already seen the nurse dan dia cakap okay, boleh relax lah. Few of my mum friends also felt the same during first trimester, siap keluar google dok carik symptoms haha! Kalau rasa extra worried atau bleeding ada, better check with your doctor again just to be sure your mind at peace je, but honestly sounds like normal pregnancy niggles. Congrats on baby!