Firstly, you did not say if this is your first pregnancy
. No worry, anyhow, because this dull ache is quite common during pregnancy. It is most often due to stretching of skin and muscle over the abdomen which leads to sensitivity. It is caused by the enlarging uterus
which gets prominent from the second trimester as in your case. This feeling is observed more in the first pregnancy as stretching of a previously taut skin occurs whereas in successive pregnancies the skin is already lax. If this ache gets worse or is associated with a backache
or discharge you should immediately see your doctor. Good luck.