Natty, how are you sitting at work? Try to make sure (I know how uncomfortable it can be) you're sitting forward in the chair, towards the front of the seat with your back straight. I also remember that I really POPPED outwards with the baby belly at that stage of my pregnancy so it could be also everything stretching - ligaments etc to accomodate your growing baby.

Good luck hon, it sounds like they're BH and you're right - they are sometimes really painful.