I had that same problem n the doctor said it was cause the baby was laying on a nerve
it was all down one side... its stopped now... took a few days to go away... being on maternity leave means lots of time to rest :)
Is it located on the edge of your ribs? I had this on my right side also and the midwife told me it was my organs rubbing, I didn't believe her as the pain never changed position it was always the same spot no matter what I did or how I moved so I went to a doctor and he told me I had strained the abdominal muscles that run down kinda from your boob along the ribs and has torn some of the muscle fibers. There's nothing they can do for it though but what I found helped me what stopped all heavy lifting I work in childcare so that meant not picking any children up and it's completely gone now since I stopped that it did take a couple weeks. Hope this helps!!