hello there
there are couple of things, i need to know before proceeding. have u got any back pain now or any pain at back along with this shin pain??. if your pain awakes in night, is it really unrelenting pain?? in that case it is serious, any history of breast cancer?? do u had any trauma??, is ur pain after exertion/activity?? is it localized or is it diffuse, i know u said as a constant pain, wat worsens the pain??, Is there anything which makes ur pain better??(ice/heat) do u run or jog?? do u get more pain after activity or during activity??.

During pregnancy its common to get sciatic pain, which is quite different from wat u r saying.. you described pain as throbbing, which is normally expressed for nervy kind of a pain.

If i am going to guess really superficially, then it can be some nervy pain(common peroneal nerve entrapment, or stress fracture( as u can localize the pain) or some activity related pain(runners shin pain)

I know too many questions..