Kelly, I'm a musculo-skeletal physio, and have also worked in women's health where I treated musculoskeletal problems in women ante- and post-natally.

The pain that dantri described, which you say is identical to yours now, sounds like a classic thoracic facet (aka zygo-pophaseal) joint or, less likely, disc dysfunction. you can think of it as the thoracic version of sciatica, where the pain in low back and refers down the back of the leg on the affected side. If I saw you in clinic I would expect to find really stiff local joint which is referring pain along the route of the nerve that exits at that level. For mid-thoracic problems, that's roughly around the line of the ribs, ie, around the chest wall and under the arm towards the front of the chest wall on that side. Treatment would be mobilisation to the affected joint/joints and exercises to maintain and improve mobility at that level, as well as postural education.

You're right in saying that sitting isn't especially good for the spine, and that counts as much for the thoracic spine as for the low back. You're also right that nurofen would likely help, but obviously it's not to be taken when pregnant! For more a more comfortable sitting position, try using a kitchen chair backwards, straddling the seat and leaning forward on to the backrest with your arms. This is good for off-loading the thoracic spine, and of course is good for optimal foetal positioning as well. Just don't try driving like this! For sitting at a desk job, or in the car, a lumbar support can help, ie, a rolled up small towel or bathmat which you lay in the inward curve of the small of your back, between your back and the backrest of your chair or carseat. It it feels too big, unroll it a turn and let the excess hang down. Try different towels/tighter or looser rolling, and rounder rolling or flatter folding until you find a shape and fatness that supports your low back without feeling excessive. A well fitted bra, where the weight of your breasts is supported significantly more by the chest band than by the shoulder straps, also can help.

To me it sounds like a very treatable problem. If your chiro visits have not helped much, you always have the option of trying a different chiro/osteo/physio instead. If paying privately is an issue, try to get a referral to your local public women's health physio clinic and see if they can help.

The good news is that this sort of problem rarely has much impact on labour and birth, though you might find that your favoured positions are partly determined by this pain as well as by the usual types of labour pains. It sometimes goes away completely or partially after delivery, but can also be aggravated by the prolonged and frequent sitting that new mum's often do when breast-feeding (and to a lesser extent bottle-feeding.) In the early weeks/months post-birth, changing breast size and weight, and the difficulty some women have in consistently wearing a well fitted, supportive bra also can make it worse. Make sure you use cushions under baby to bring baby up to boob, and don't slouch down to bring boob to baby, and use that lumbar support whenever you sit to feed. Definitely ask for a referral from your mw or GP to a postnatal physio if the pain persists beyond the birth.

I hope that helps you cope with the last few weeks.