pressure in pelvis at 15 weeks

Dr. and ladies. I have been feeling this pressure in the area right above my hair line. It is not painful but feels like I worked those muscles or a dull pressure. I thought it could ligament pain but it is constant and not a stabbing pain...not is it on the sides. One of my papers from the dr said abdmoinal pain could be a sign or pre-term labor. Does this sound like ligament pressure or should I call my dr.???