I am 16-weeks pregnant and have been having periodic pain in the middle of my lower abdomen. I usually feel it when I lean forward real far (like when I am standing up from sitting or getting out of a car). It is different than the round ligament pain I get on my sides. I have been having it on and off for two weeks. I don't have any other symptoms of a bladder infection such as frequent urination.
It still sounds like ligament pain (there are lots!), otherwise known as "growing pains." They are very common around the belly button as you get close to 20 weeks. You are just quicker than most!
-- Cynthia, CNM. PhD.