Round Ligament Pain
Your have round ligaments in your pelvis that hold and support your uterus. During pregnancy as your uterus grows these round ligaments will stretch and thicken to support the uterus. The pain can feel like a dull ache or even sharp jabbing pains. The pain usually worsens when you move into different positions or when you are in one position for too long.
For me these pains were the primary cause of cramping and pain during my first and second trimester. Putting warm pack on the sides of my belly and supporting my belly helped to ease the pain.
As with anything else, please call your doctor if the pain worsen or if you are concerned.