I have no clue, mine is hurting right above my belly button. :/
Mine was the same! I thought it was because my stomach and bowel were being pushed up by the uterus. I dont know if that was the reason though.Also because my waist was widening I could see the button of my belly button easily. So maybe because its getting stretched
My belly button hurt for a couple of weeks and then just went away. Some people have a hernia though, so you need to let your Dr know asap. Hopefully it's just stretching though! =)